APPLICATION NOTE AN10216-01 I

APPLICATION NOTE  AN10216-01 I
AN10216-01 I2C Manual
INTEGRATED CIRCUITS
APPLICATION NOTE
AN10216-01
I2C MANUAL
Abstract – The I2C Manual provides a broad overview of the various serial buses,
why the I2C bus should be considered, technical detail of the I2C bus and how it
works, previous limitations/solutions, comparison to the SMBus, Intelligent Platform
Management Interface implementations, review of the different I2C devices that are
available and patent/royalty information. The I2C Manual was presented during the 3
hour TecForum at DesignCon 2003 in San Jose, CA on 27 January 2003.
Jean-Marc Irazabal – I2C Technical Marketing Manager
Steve Blozis – I2C International Product Manager
Specialty Logic Product Line
Logic Product Group
Philips Semiconductors
March 24, 2003
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AN10216-01 I2C Manual
TABLE OF CONTENTS
TABLE OF CONTENTS ...................................................................................................................................................2
OVERVIEW .......................................................................................................................................................................4
DESCRIPTION .....................................................................................................................................................................4
SERIAL BUS OVERVIEW...............................................................................................................................................4
UART OVERVIEW.............................................................................................................................................................6
SPI OVERVIEW..................................................................................................................................................................6
CAN OVERVIEW ...............................................................................................................................................................7
USB OVERVIEW................................................................................................................................................................9
1394 OVERVIEW .............................................................................................................................................................10
I2C OVERVIEW ................................................................................................................................................................11
SERIAL BUS COMPARISON SUMMARY .............................................................................................................................12
I2C THEORY OF OPERATION ....................................................................................................................................13
I2C BUS TERMINOLOGY...................................................................................................................................................13
START AND STOP CONDITIONS ....................................................................................................................................14
HARDWARE CONFIGURATION ...............................................................................................................................14
BUS COMMUNICATION.............................................................................................................................................14
TERMINOLOGY FOR BUS TRANSFER ................................................................................................................................15
I2C DESIGNER BENEFITS .................................................................................................................................................17
I2C MANUFACTURERS BENEFITS .....................................................................................................................................17
OVERCOMING PREVIOUS LIMITATIONS .............................................................................................................18
ADDRESS CONFLICTS ......................................................................................................................................................18
CAPACITIVE LOADING > 400 PF (ISOLATION) .................................................................................................................19
VOLTAGE LEVEL TRANSLATION .....................................................................................................................................20
INCREASE I2C BUS RELIABILITY (SLAVE DEVICES).........................................................................................................21
INCREASING I2C BUS RELIABILITY (MASTER DEVICES)..................................................................................................22
CAPACITIVE LOADING > 400 PF (BUFFER)......................................................................................................................22
LIVE INSERTION INTO THE I2C BUS .................................................................................................................................24
LONG I2C BUS LENGTHS .................................................................................................................................................25
PARALLEL TO I2C BUS CONTROLLER ..............................................................................................................................25
DEVELOPMENT TOOLS AND EVALUATION BOARD OVERVIEW..................................................................26
PURPOSE OF THE DEVELOPMENT TOOL AND I2C EVALUATION BOARD ...........................................................................26
WIN-I2CNT SCREEN EXAMPLES.....................................................................................................................................28
HOW TO ORDER THE I2C 2002-1A EVALUATION KIT .....................................................................................................31
COMPARISON OF I2C WITH SMBUS ........................................................................................................................31
I2C/SMBUS COMPLIANCY ...............................................................................................................................................31
DIFFERENCES SMBUS 1.0 AND SMBUS 2.0 ....................................................................................................................32
INTELLIGENT PLATFORM MANAGEMENT INTERFACE (IPMI) ....................................................................32
INTEL SERVER MANAGEMENT.........................................................................................................................................33
PICMG ...........................................................................................................................................................................33
VMEBUS .........................................................................................................................................................................34
I2C DEVICE OVERVIEW ..............................................................................................................................................35
TV RECEPTION................................................................................................................................................................36
RADIO RECEPTION ..........................................................................................................................................................36
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AN10216-01 I2C Manual
AUDIO PROCESSING ........................................................................................................................................................37
DUAL TONE MULTI-FREQUENCY (DTMF)......................................................................................................................37
LCD DISPLAY DRIVER ....................................................................................................................................................37
LIGHT SENSOR ................................................................................................................................................................38
REAL TIME CLOCK/CALENDAR .......................................................................................................................................38
GENERAL PURPOSE I/O EXPANDERS ...............................................................................................................................38
LED DIMMERS AND BLINKERS .......................................................................................................................................40
DIP SWITCH ....................................................................................................................................................................42
MULTIPLEXERS AND SWITCHES.......................................................................................................................................43
VOLTAGE LEVEL TRANSLATORS .....................................................................................................................................45
BUS REPEATERS AND HUBS ............................................................................................................................................45
HOT SWAP BUS BUFFERS ................................................................................................................................................45
BUS EXTENDERS .............................................................................................................................................................46
ELECTRO-OPTICAL ISOLATION ........................................................................................................................................47
RISE TIME ACCELERATORS .............................................................................................................................................47
PARALLEL BUS TO I2C BUS CONTROLLER ......................................................................................................................48
DIGITAL POTENTIOMETERS .............................................................................................................................................48
ANALOG TO DIGITAL CONVERTERS ................................................................................................................................48
SERIAL RAM/EEPROM .................................................................................................................................................49
HARDWARE MONITORS/TEMP & VOLTAGE SENSORS .....................................................................................................49
MICROCONTROLLERS ......................................................................................................................................................49
I2C PATENT AND LEGAL INFORMATION ..............................................................................................................50
ADDITIONAL INFORMATION ...................................................................................................................................50
APPLICATION NOTES..................................................................................................................................................50
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AN10216-01 I2C Manual
OVERVIEW
Description
Philips Semiconductors developed the I2C bus over 20 years ago and has an extensive collection of specific use and
general purpose devices. This application note was developed from the 3 hour long I2C Overview TecForum presentation
at DesignCon 2003 in San Jose, CA on 27 January 2003 and provides a broad overview of how the I2C bus compares to
other serial buses, how the I2C bus works, ways to overcome previous limitations, new uses of I2C such as in the
Intelligent Platform Management Interface, overview of the various different categories of I2C devices and patent/royalty
information. Full size Slides are posted as a PDF file on the Philips Logic I2C collateral web site as DesignCon 2003
TecForum I2C Bus Overview PDF file. Place holder and title slides have been removed from this application note and
some slides with all text have been incorporated into the application note speaker notes.
three shared signal lines, for bit timing, data, and R/W.
The selection of communicating partners is made with
one separate wire for each chip. As the number of chips
grows, so do the selection wires. The next stage is to
use multiplexing of the selection wires and call them an
address bus.
Serial Bus Overview
Co
m
m
un
ic
at
io
n
er
sum
Con
s
If there are 8 address wires we can select any one of
256 devices by using a ‘one of 256’ decoder IC. In a
parallel bus system there could be 8 or 16 (or more)
data wires. Taken to the next step, we can share the
function of the wires between addresses and data but it
starts to take quite a bit of hardware and worst is, we
still have lots of wires. We can take a different
approach and try to eliminate all except the data wiring
itself. Then we need to multiplex the data, the selection
(address), and the direction info - read/write. We need
to develop relatively complex rules for that, but we save
on those wires. This presentation covers buses that use
only one or two data lines so that they are still attractive
for sending data over reasonable distances - at least a
few meters, but perhaps even km.
IEEE1394
e
otiv
om
t
u
A
SERIAL
BUSES
UART
In
du
s
SPI
tri
a
l
BUS
DesignCon 2003 TecForum I2C Bus Overview
5
Slide 5
General concept for Serial communications
SCL
DATA
Shift Register
Parallel to Serial
SDA
select 3
select 2
select 1
READ
or
WRITE?
“MASTER”
Typical Signaling Characteristics
enable
R/W
Shift Reg#
// to Ser.
SLAVE 1
enable
R/W
Shift Reg#
// to Ser.
SLAVE 2
enable
R/W
Shift Reg#
// to Ser.
SLAVE 3
LVTTL
• A point to point communication does not require a Select control signal
• An asynchronous communication does not have a Clock signal
I2C SMBus
• Data, Select and R/W signals can share the same line, depending on the protocol
PECL
LVPECL LVDS
• Notice that Slave 1 cannot communicate with Slave 2 or 3 (except via the ‘master’)
Only the ‘master’ can start communicating. Slaves can ‘only speak when spoken to’
DesignCon 2003 TecForum I2C Bus Overview
I2C
RS422/485
6
I2C
1394
GTL+
CML
LVT
LVC
Slide 6
DesignCon 2003 TecForum I2C Bus Overview
Buses come in two forms, serial and parallel. The data
and/or addresses can be sent over 1 wire, bit after bit, or
over 8 or 32 wires at once. Always there has to be some
way to share the common wiring, some rules, and some
synchronization. Slide 6 shows a serial data bus with
5V
3.3 V
2.5 V
GTL
GTLP
7
Slide 7
Devices can communicate differentially or single ended
with various signal characteristics as shown in Slide 7.
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AN10216-01 I2C Manual
also because it may be used within the PC software as a
general data path that USB drivers can use.
Transmission Standards
Terminology for USB: The use of older terms such as
the spec version 1.1 and 2.0 is now discouraged. There
is just “USB” (meaning the original 12 Mbits/sec and
1.5 Mbits/sec speeds of USB version 1.1) and Hi-Speed
USB meaning the faster 480 Mbits/sec option included
in spec version 2.0. Parts conforming to or capable of
the 480 Mbits/sec are certified as Hi-Speed USB and
will then feature the logo with the red stripe “Hi-Speed”
fitted above the standard USB logo. The reason to avoid
use of the new spec version 2.0 as a generic name is
that this version includes all the older versions and
speeds as well as the new Hi-Speed specs. So USB 2.0
compliance does NOT imply Hi-Speed (480 Mbits/sec).
ICs can be compliant with USB 2.0 specifications yet
only be capable of the older ‘full speed’ or 12
Mbits/sec.
Data Transfer Rate (Mbps)
2500
CML
655
400
GTLP
BTL
ETL
1394.a
LVD
ECL S =RS-6
/PEC
4
L/LV 4
PEC
L
35
10
General
Purpose 1
Logic
RS-422
RS-485
0.1
I2C
0.5
RS-423
RS-232
0
10
Backplane Length (meters)
100
1000
Cable Length (meters)
DesignCon 2003 TecForum I2C Bus Overview
8
Slide 8
The various data transmission rates vs length or cable
or backplane length of the different transmission
standards are shown in Slide 8.
Bus characteristics compared
Speed of various connectivity methods (bits/sec)
CAN (1 Wire)
I2C (‘Industrial’, and SMBus)
SPI
CAN (fault tolerant)
I2C
CAN (high speed)
I2C ‘High Speed mode’
USB (1.1)
SCSI (parallel bus)
Fast SCSI
Ultra SCSI-3
Firewire / IEEE1394
Hi-Speed USB (2.0)
33 kHz (typ)
100 kHz
110 kHz (original speed)
125 kHz
400 kHz
1 MHz
3.4 MHz
1.5 MHz or 12 MHz
40 MHz
8-80 MHz
18-160 MHz
400 MHz
480 MHz
Bu s
Data rat e
(bits / sec)
Len gth
( meter s)
Length limiting f actor
No d es
Typ.number
I2 C
400k
2
w iring capacitance
20
Node number
limiting f actor
400pF max
I2C w ith buf fer
400k
100
propagation delays
an y
no limit
I2 C high speed
3.4M
0.5
w iring capacitance
5
100pF max
CAN 1 w ire
33k
100
total capacitance
32
5k
10km
CA N diff erential
125k
500
propagation delays
100
1M
40
USB (low - speed, 1.1)
1.5M
USB ( full - speed, 1.1)
1.5/12M
Hi- Spe ed USB (2.0)
480M
IEEE-1394
100 to 400M+
load resistance and
transceiver cur r ent
drive
3
cable specs
2
bus specs
25
5 cables linking 6 nodes
( 5m cable node to node)
127
bus and hub specs
72
16 hops, 4.5M each
63
6-bit address
DesignCon 2003 TecForum I2C Bus Overview
10
Slide 10
DesignCon 2003 TecForum I2C Bus Overview
9
In Slide 10 we look at three important characteristics:
• Speed, or data rate
• Number of devices allowed to be connected (to
share the bus wires)
• Total length of the wiring
Slide 9
Increasing fast serial transmission specifications are
shown in Slide 9. Proper treatment of the 480 MHz
version of USB - trying to beat the emerging 400 MHz
1394a spec - that is looking to an improved ‘b’ spec - etc is beyond the scope of this presentation. Philips is
developing leading-edge components to support both
USB and 1394 buses.
Numbers are supposed to be realistic estimates but are
based on meeting bus specifications. But rules are made
to be broken! When buffered, I2C can be limited by
wiring propagation delays but it is still possible to run
much longer distances by using slower clock rates and
maybe also compromising the bus rise and fall-time
specifications on the buffered bus because it is not
bound to conform to I2C specifications.
Today the path forward in USB is built on “OTG” (On
The Go) applications but the costs and complexity of
this are probably beyond the limits of many customers.
If designers are identified as designing for large
international markets then please contact the USB
group for additional support, particularly of Host and
OTG solutions. Apologies for inclusion of the parallel
SCSI bus. It is intended for comparison purposes and
The figure in Slide 10 limiting I2C range by
propagation delays is conservative and allows for
published response delays in chips like older E2
memories. Measured chip responses are typically <
700 ns and that allows for long cable delays and/or
5
AN10216-01 I2C Manual
all the bits and rebuilds the (parallel) byte and puts it in
a buffer.
operation well above 100 kHz with the P82B96. The
theoretical round-trip delay on 100 m of cable is only
approx 1 µs and the maximum allowed delay, assuming
zero delays in ICs, is about 3 µs at 100 kHz. The
figures for CAN are not quite as conservative; they are
the ‘often quoted values’. The round trip delay in 10
km cable is about 0.1 ms while 5 kbps implies 0.2 ms
nominal bit time, and a need to sample during the
second half of the bit time. That is under the user’s
control, but needs attention.
Along with converting between serial and parallel, the
UART does some other things as a byproduct (side
effect) of its primary task. The voltage used to represent
bits is also converted (changed). Extra bits (called start
and stop bits) are added to each byte before it is
transmitted. Also, while the flow rate (in bytes/s) on the
parallel bus speed inside the computer is very high, the
flow rate out the UART on the serial port side of it is
much lower. The UART has a fixed set of rates
(speeds) that it can use at its serial port interface.
USB 2 and IEEE-1394 are still ‘emerging standards’.
Figures quoted may not be practical; they are just based
on the specification restrictions.
UART - Applications
UART Overview
tt
Datacom
Datacom r
r
controller
controller x
x
(Universal Asynchronous Receiver Transmitter)
•
•
•
•
Communication standard implemented in the 60’s.
Simple, universal, well understood and well supported.
Slow speed communication standard: up to 1 Mbits/s
Asynchronous means that the data clock is not included in
the data: Sender and Receiver must agree on timing
parameters in advance.
• “Start” and “Stop” bits indicates the data to be sent
• Parity information can also be sent
0
Start bit
1
2
3
4
5
8 Bit Data
DesignCon 2003 TecForum I2C Bus Overview
6
Public
/ Private
LAN
application
Telephone / Internet
Network
Serial Interface
Server
Server
Processor
Processor Digital
What is UART?
t
rModem
Modem
x
Analog or Digital
WAN application
Parallel
Interface
tt
Modem
Modemrr
xx
Client
Client
Processor
Processor
tt
Datacom
rr Datacom
controller
xx controller
Serial Interface
Appliance Terminals
• Entertainment
• Home Security
Cash
register
Display
Address
Micro
Micro Data
contr.
contr.
UART
Interface to
Server
Memory
Memory
DUART
DUART
SC28L92
SC28L92
• Robotics
• Automotive
• Cellular
• Medical
Bar code
reader
2
DesignCon 2003 TecForum I C Bus Overview
Printer
7
Stop bit
Parity Information
12
Slide 12
11
SPI Overview
Slide 11
What is SPI?
UARTs
(Universal
Asynchronous
Receiver
Transmitter) are serial chips on your PC motherboard
(or on an internal modem card). The UART function
may also be done on a chip that does other things as
well. On older computers like many 486's, the chips
were on the disk IO controller card. Still older
computers have dedicated serial boards.
• Serial Peripheral Interface (SPI) is a 4-wire full-duplex
synchronous serial data link:
–
–
–
–
SCLK: Serial Clock
MOSI: Master Out Slave In - Data from Master to Slave
MISO: Master In Slave Out - Data from Slave to Master
SS: Slave Select
• Originally developed by Motorola
• Used for connecting peripherals to each other and to
microprocessors
• Shift register that serially transmits data to other SPI devices
• Actually a “3 + n” wire interface with n = number of devices
• Only one master active at a time
• Various Speed transfers (function of the system clock)
The UARTs purpose is to convert bytes from the PC's
parallel bus to a serial bit-stream. The cable going out
of the serial port is serial and has only one wire for each
direction of flow. The serial port sends out a stream of
bits, one bit at a time. Conversely, the bit stream that
enters the serial port via the external cable is converted
to parallel bytes that the computer can understand.
UARTs deal with data in byte-sized pieces, which is
conveniently also the size of ASCII characters.
DesignCon 2003 TecForum I2C Bus Overview
13
Slide 13
The Serial Peripheral Interface (SPI) circuit is a
synchronous serial data link that is standard across
many Motorola microprocessors and other peripheral
chips. It provides support for a high bandwidth (1 mega
baud) network connection amongst CPUs and other
devices supporting the SPI.
Say you have a terminal hooked up to your PC. When
you type a character, the terminal gives that character to
its transmitter (also a UART). The transmitter sends
that byte out onto the serial line, one bit at a time, at a
specific rate. On the PC end, the receiving UART takes
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AN10216-01 I2C Manual
synchronized by the serial clock (SCLK). One bit of
data is transferred for each clock cycle. Four clock
modes are defined for the SPI bus by the value of the
clock polarity and the clock phase bits. The clock
polarity determines the level of the clock idle state and
the clock phase determines which clock edge places
new data on the bus. Any hardware device capable of
operation in more than one mode will have some
method of selecting the value of these bits.
SPI - How are the connected devices recognized?
SCLK
MOSI
MISO
SS 1
SCLK
MOSI
MISO
SS
SLAVE 1
SCLK
MOSI
MISO
SS
SLAVE 2
SCLK
MOSI
MISO
SS
SLAVE 3
SS 2
SS 3
MASTER
CAN Overview
• Simple transfer scheme, 8 or 16 bits
• Allows many devices to use SPI through the addition of a shift register
What is CAN ? (Controller Area Network)
• Full duplex communications
• Number of wires proportional to the number of devices in the bus
DesignCon 2003 TecForum I2C Bus Overview
• Proposed by Bosch with automotive applications in mind
(and promoted by CIA - of Germany - for industrial
applications)
• Relatively complex coding of the messages
• Relatively accurate and (usually) fixed timing
• All modules participate in every communication
• Content-oriented (message) addressing scheme
14
Slide 14
The SPI is essentially a “three-wire plus slave selects”
serial bus for eight or sixteen bit data transfer
applications. The three wires carry information between
devices connected to the bus. Each device on the bus
acts simultaneously as a transmitter and receiver. Two
of the three lines transfer data (one line for each
direction) and the third is a serial clock. Some devices
may be only transmitters while others only receivers.
Generally, a device that transmits usually possesses the
capability to receive data also. An SPI display is an
example of a receive-only device while EEPROM is a
receiver and transmit device.
The devices connected to the SPI bus may be classified
as Master or Slave devices. A master device initiates an
information transfer on the bus and generates clock and
control signals. A slave device is controlled by the
master through a slave select (chip enable) line and is
active only when selected. Generally, a dedicated select
line is required for each slave device. The same device
can possess the functionality of a master and a slave but
at any point of time, only one master can control the
bus in a multi-master mode configuration. Any slave
device that is not selected must release (make it high
impedance) the slave output line.
The SPI bus employs a simple shift register data
transfer scheme: Data is clocked out of and into the
active devices in a first-in, first-out fashion. It is in this
manner that SPI devices transmit and receive in full
duplex mode.
All lines on the SPI bus are unidirectional: The signal
on the clock line (SCLK) is generated by the master and
is primarily used to synchronize data transfer. The
master-out, slave-in (MOSI) line carries data from the
master to the slave and the master-in, slave-out (MISO)
line carries data from the slave to the master. Each
slave device is selected by the master via individual
select lines. Information on the SPI bus can be
transferred at a rate of near zero bits per second to 1
Mbits per second. Data transfer is usually performed in
eight/sixteen bit blocks. All data transfer is
Filter
Filter
Frame
DesignCon 2003 TecForum I2C Bus Overview
15
Slide 15
CAN objective is to achieve reliable communications in
relatively critical control system applications e.g.
engine management or anti-lock brakes. There are
several aspects to reliability - availability of the bus
when important data needs to be sent, the possibility of
bits in a message being corrupted by noise etc., and
electrical/mechanical failure modes in the wiring.
At least a ceramic resonator and possibly a quartz
crystal are needed to generate the accurate timing
needed. The clock and data are combined and 6 ‘high’
bits in succession is interpreted as a bus error. So the
clock and bit timings are important. All connected
modules must use the same timings. All modules are
looking for any error in the data at any point on the
wiring and will report that error so the message can be
re-sent etc.
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AN10216-01 I2C Manual
Start Of Frame
CAN Bus Advantages
CAN protocol
• Accepted standard for Automotive and industrial applications
Identifier
Remote Transmission Request
Identifier Extension
Data Length Code
Data
– interfacing between various vendors easier to implement
• Freedom to select suitable hardware
– differential or 1 wire bus
Cyclic Redundancy Check
Acknowledge
End Of Frame
Intermission Frame
Space
• Secure communications, high Level of error detection
–
–
–
–
–
• High degree of EMC immunity (when using Si-On-Insulator
technology)
• Very intelligent controller requested to generate such protocol
DesignCon 2003 TecForum I2C Bus Overview
15 bit CRC messages (Cyclic Redundancy Check)
Reporting / logging
Faulty devices can disconnect themselves
Low latency time
Configuration flexibility
DesignCon 2003 TecForum I2C Bus Overview
16
17
Slide 16
Slide 17
Like I2C, the CAN bus wires are pulled by resistors to
their resting state called a ‘recessive’ state. When a
transceiver drives the bus it forces a voltage called the
‘dominant’ state. The identifier indicates the meaning
of the data, not the intended recipient. So all nodes
receive and ‘filter’ this identifier and can decide
whether to act on the data or not. So the bus is using
‘multicast’ - many modules can act on the message, and
all modules are checking the message for transmission
errors. Arbitration is ‘bit wise’ like I2C - the module
forcing a ‘1’ beats a module trying for a ‘0’ and the
loser withdraws to try again later.
I2C products from many manufacturers are all
compatible but CAN hardware will be selected and
dedicated for each particular system design. Some CAN
transceivers will be compatible with others, but that is
more likely to be the exception than the rule. CAN
designs are usually individual systems that are not
intended to be modified. Philips parts greatly enhance
the feature of reliability by their ability to use partbroken bus wiring and disconnect themselves if they are
recording too many bus errors.
-
-
There are several aspects to reliability - availability of
the bus when important data needs to be sent, the
possibility of bits in a message being corrupted by noise
etc., and the consequences of electrical/mechanical
failure modes in the wiring. All these aspects are treated
seriously by the CAN specifications and the suppliers
of the interface ICs - for example Philips believes
conventional high voltage IC processes are not good
enough and uses Silicon-on-insulator technology to
increase ruggedness and avoid the alternative of using
common-mode chokes for protection. To give an
example of immunity, a transceiver on 5 V must be able
to cope with jump-start and load-dump voltages on its
supply or bus wires. That is 40 V on the supply and +/40 V on the bus lines, plus transients of –150 V/+100 V
capacitively coupled from a pulse generator in a test
circuit!
DLC: data length code
CRC: cyclic redundancy check (remainder of a
division calculation). All devices that pass the CRC
will acknowledge or will generate an error flag
after the data frame finishes.
ACK: acknowledge.
Error frame: (at least) 6 consecutive dominant bits
then 7 recessive bits.
A message ‘filter’ can be programmed to test the 11-bit
identifier and one or two bytes of the data (In general
up to 32 bits) to decide whether to accept the message
and issue an interrupt. It could also look at all of the
29-bit identifier.
8
AN10216-01 I2C Manual
USB Overview
USB Bus Advantages
What is USB ? (Universal Serial Bus)
•
•
•
•
•
•
•
•
•
•
•
•
Originally a standard for connecting PCs to peripherals
Defined by Intel, Microsoft, …
Intended to replace the large number of legacy ports in the PC
Single master (= Host) system with up to 127 peripherals
Simple plug and play; no need to open the PC
Standardized plugs, ports, cables
Has over 99% penetration on all new PCs
Adapting to new requirements for flexibility of Host function
Hot pluggable, no need to open cabinets
Automatic configuration
Up to 127 devices can be connected together
Push for USB to become THE standard on PCs
– standard for iMac, supported by Windows, now on > 99%of PCs
• Interfaces (bridges) to other communication channels
exist
– USB to serial port (serial port vanishing from laptops)
– USB to IrDA or to Ethernet
• Extreme volumes force down IC and hardware prices
• Protocol is evolving fast
– New Hardware/Software allows dynamic exchanging of Host/Slave
roles
– PC is no longer the only system Host. Can be a camera or a printer.
DesignCon 2003 TecForum I2C Bus Overview
DesignCon 2003 TecForum
I2C
Bus Overview
20
18
Slide 20
Slide 18
USB aims at mass-market products and design-ins may
be less convenient for small users. The serial port is
vanishing from the laptop and gone from iMac. There
are hardware bridges available from USB to other
communication channels but there can be higher power
consumption to go this way. Philips is innovating its
USB products to minimize power and offer maximum
flexibility in system design.
USB is the most complex of the buses presented here.
While its hardware and transceivers are relatively
simple, its software is complex and is able to efficiently
service many different applications with very different
data rates and requirements. It has a 12 Mbps rate (with
200 Mbps planned) over a twisted pair with a 4-pin
connector (2 wires are power supply). It also is limited
to short distances of at most 5 meters (depends on
configuration). Linux supports the bus, although not all
devices that can plug into the bus are supported. It is
synchronous and transmits in special packets like a
network. Just like a network, it can have several devices
attached to it. Each device on it gets a time-slice of
exclusive use for a short time. A device can also be
guaranteed the use of the bus at fixed intervals. One
device can monopolize it if no other device wants to use
it.
Versions of USB specification
• USB 1.1
– Established, large PC peripheral markets
– Well controlled hardware, special 4-pin plugs/sockets
– 12MBits/sec (normal) or 1.5Mbits/sec (low speed) data rate
• USB 2.0
– Challenging IEEE1394/Firewire for video possibilities
– 480 MHz clock for Hi-Speed means it’s real “UHF” transmission
– Hi-Speed option needs more complex chip hardware and software
– Hi-Speed component prices about x 2 compared to full speed
• USB “OTG” (On The Go) Supplement
– New hardware - smaller 5-pin plugs/sockets
– Lower power (reduced or no bus-powering)
USB Topology (original concept, USB1.1, USB2.0)
¾ Host
Monitor
− One PC host per system
− Provides power to peripherals
¾ Hub
Host
PC
− Provides ports for connecting more
peripheral devices.
− Provides power, terminations
5m
5m
5m
5m
DesignCon 2003 TecForum I2C Bus Overview
Hub
Slide 21
5m
For USB 1.1 and 2.0 the hardware is well established.
The shape of the plug/socket at Host end is different
from the shape at the peripheral end. USB is always a
single point-to-point link over the cable. To allow
connection of multiple peripherals a HUB is introduced.
The Hub functions to multiplex the data from the
‘downstream’ peripherals into one ‘upstream’ data
linkage to the Host. In Hi-Speed systems it is necessary
for the system to start communicating as a normal USB
1.1 system and then additional hardware (faster
transceivers etc) is activated to allow a higher speed.
The Hi-Speed system is much more complex
(hardware/software) than normal USB (1.1). For USB
− External supply or Bus Powered
¾ Device, Interfaces and Endpoints
− Device is a collection of data
interface(s)
Device
− Interface is a collection of
endpoints (data channels)
− Endpoint associated with FIFO(s) for data I/O interfacing
DesignCon 2003 TecForum I2C Bus Overview
21
19
Slide 19
Slide 19 shows a typical USB configuration.
9
AN10216-01 I2C Manual
specified to well over 1A at 8-30 volts (approx) leading to some unkind references to a ‘fire’ wire!
and Hi-Speed the development of ‘stand-alone’ Host
ICs such as ISP1161 and ISP1561 allowed the Host
function to be embedded in products such as Digital
Still Cameras or printers so that more direct transfer of
data was possible without using the path Camera → PC
→ Printer under control of the PC as the host. That two
step transfer involves connecting the camera to the PC
(one USB cable) and also the PC to the printer (second
USB cable). The goal is to do without the PC.
1394 software or message format consists of timeslots
within which the data is sent in blocks or ‘channels’.
For real-time data transfer it is possible to guarantee the
availability of one or more channels to guarantee a
certain data rate. This is important for video because
it’s no good sending a packet of corrected data after a
blank has appeared on the screen!
The next step involved the shrinking of the USB
connector hardware, to make it more compatible with
small products like digital cameras, and making
provision (extra pin) for dynamic exchanging of Host
and slave device functions without removing the USB
cable for reversing the master/slave connectors. The
new hardware and USB specification version is called
“On The Go” (OTG). The OTG specification no longer
requires the Host to provide the 1/2 A power supply to
peripherals and indeed allows arbitration to determine
whether Host or peripheral (or neither) will provide the
system power.
Microsoft says,
“IEEE 1394 defines a single
interconnection bus that serves many purposes and user
scenarios. In addition to its adoption by the consumer
electronics industry, PC vendors—including Compaq,
Dell, IBM, Fujitsu, Toshiba, Sony, NEC, and
Gateway—are now shipping Windows-based PCs with
1394 buses.
The IEEE 1394 bus complements the Universal Serial
Bus (USB) and is particularly optimized for connecting
digital media devices and high-speed storage devices to
a PC. It is a peer-to-peer bus. Devices have more builtin intelligence than USB devices, and they run
independently of the processor, resulting in better
performance.
1394 Overview
What is IEEE1394 ?
The 100-, 200-, and 400-Mbps transfer rates currently
specified in the IEEE 1394a standard and the proposed
enhancements in 1394b are well suited to meeting the
throughput requirements of multiple streaming
input/output devices connected to a single PC. The
licensing fee for use of patented IEEE 1394 technology
has been established at US $0.25 per system.
• A bus standard devised to handle the high data throughput
requirements of MPEG-2 and DVD
– Video requires constant transfer rates with guaranteed bandwidth
– Data rates 100, 200, 400 Mbits/sec and looking to 3.2 Gb/s
• Also known as “Firewire” bus (registered trademark of Apple)
• Automatically re-configures itself as each device is added
– True plug & play
– Hot-plugging of devices allowed
• Up to 63 devices, 4.5 m cable ‘hops’, with max. 16 hops
• Bandwidth guaranteed
DesignCon 2003 TecForum I2C Bus Overview
With connectivity for storage, scanners, printers, and
other types of consumer A/V devices, IEEE 1394 gives
users all the benefits of a great legacy-free connector—
a true Plug and Play experience and hassle-free PC
connectivity.”
22
Slide 22
1394 Topology
1394 may claim to be more proven or established than
USB but both are ‘emerging’ specifications that are
trying to out-do each other! Philips strongly supports
BOTH. 1394 was chosen by Philips as the bus to link
set-top boxes, DVD, and digital TVs. 1394 has an ’a’
version taking it to 400 Mb/sec and more recently a ‘b’
version for higher speed and to allow longer cable runs,
perhaps 100 meter hops!
• Physical layer
– Analog interface to the cable
– Simple repeater
– Performs bus arbitration
• Link layer
1394 sends information over a PAIR of twisted pairs.
One for data, the other is the clocking strobe. The clock
is simply recovered by an Ex-Or of the data and strobe
line signals. No PLL is needed. There is provision for
lots of remote device powering via the cable if the 6-pin
plug connection version is used. The power wires are
– Assembles and dis-assembles bus packets
– Handles response and acknowledgment functions
• Host controller
– Implements higher levels of the protocol
DesignCon 2003 TecForum I2C Bus Overview
Slide 23
10
23
AN10216-01 I2C Manual
I2C Overview
•
What is I2C ? (Inter-IC)
• Originally, bus defined by Philips providing a simple way to
talk between IC’s by using a minimum number of pins
• A set of specifications to build a simple universal bus
guaranteeing compatibility of parts (ICs) from different
manufacturers:
•
– Simple Hardware standards
– Simple Software protocol standard
•
• No specific wiring or connectors - most often it’s just PCB
tracks
• Has become a recognised standard throughout our industry
and is used now by ALL major IC manufacturers
DesignCon 2003 TecForum I2C Bus Overview
•
•
24
Slide 24
Originally, the I2C bus was designed to link a small
number of devices on a single card, such as to manage
the tuning of a car radio or TV. The maximum
allowable capacitance was set at 400 pF to allow proper
rise and fall times for optimum clock and data signal
integrity with a top speed of 100 kbps. In 1992 the
standard bus speed was increased to 400 kbps, to keep
up with the ever-increasing performance requirements
of new ICs. The 1998 I2C specification, increased top
speed to 3.4 Mbits/sec. All I2C devices are designed to
be able to communicate together on the same two-wire
bus and system functional architecture is limited only
by the imagination of the designer.
Each device connected to the bus is software
addressable by a unique address and simple
master/slave relationships exist at all times;
masters can operate as master-transmitters or as
master-receivers.
It’s a true multi-master bus including collision
detection and arbitration to prevent data corruption
if two or more masters simultaneously initiate data
transfer.
Serial, 8-bit oriented, bi-directional data transfers
can be made at up to 100 kbit/s in the Standardmode, up to 400 kbit/s in the Fast-mode, or up to
3.4 Mbit/s in the High-speed mode.
On-chip filtering (50 ns) rejects spikes on the bus
data line to preserve data integrity.
The number of ICs that can be connected to the
same bus segment is limited only by the maximum
bus capacitive loading of 400 pF.
I2C Bus - Software
• Simple procedures that allow communication to start, to
achieve data transfer, and to stop
–
–
–
–
–
Described in the Philips protocol (rules)
Message serial data format is very simple
Often generated by simple software in general purpose micro
Dedicated peripheral devices contain a complete interface
Multi-master capable with arbitration feature
• Each IC on the bus is identified by its own address code
– Address has to be unique
• The master IC that initiates communication provides the clock
signal (SCL)
– There is a maximum clock frequency but NO MINIMUM SPEED
But while its application to bus lengths within the
confines of consumer products such as PCs, cellular
phones, car radios or TV sets grew quickly, only a few
system integrators were using it to span a room or a
building. The I2C bus is now being increasingly used in
multiple card systems, such as a blade servers, where
the I2C bus to each card needs to be isolatable to allow
for card insertion and removal while the rest of the
system is in operation, or in systems where many more
devices need to be located onto the same card, where
the total device and trace capacitance would have
exceeded 400 pF.
DesignCon 2003 TecForum I2C Bus Overview
25
Slide 25
I2C Communication Procedure
One IC that wants to talk to another must:
1) Wait until it sees no activity on the I2C bus. SDA
and SCL are both high. The bus is 'free'.
2) Put a message on the bus that says 'its mine' - I
have STARTED to use the bus. All other ICs then
LISTEN to the bus data to see whether they might
be the one who will be called up (addressed).
3) Provide on the CLOCK (SCL) wire a clock signal.
It will be used by all the ICs as the reference time
at which each bit of DATA on the data (SDA) wire
will be correct (valid) and can be used. The data on
the data wire (SDA) must be valid at the time the
clock wire (SCL) switches from 'low' to 'high'
voltage.
4) Put out in serial form the unique binary 'address'
(name) of the IC that it wants to communicate
with.
5) Put a message (one bit) on the bus telling whether
it wants to SEND or RECEIVE data from the other
chip. (The read/write wire is gone!)
New bus extension & control devices help expand the
I2C bus beyond the 400 pF limit of about 20 devices
and allow control of more devices, even those with the
same address. These new devices are popular with
designers as they continue to expand and increase the
range of use of I2C devices in maintenance and control
applications.
I2C Features
• Only two bus lines are required: a serial data line
(SDA) and a serial clock line (SCL).
11
AN10216-01 I2C Manual
But several Masters could control one Slave, at
different times. Any ‘smart’ communications must be
via the transferred DATA, perhaps used as address info.
The I2C bus protocol does not allow for very complex
systems. It’s a ‘keep it simple’ bus. But of course
system designers are free to innovate to provide the
complex systems - based on the simple bus.
6) Ask the other IC to ACKNOWLEDGE (using one
bit) that it recognized its address and is ready to
communicate.
7) After the other IC acknowledges all is OK, data
can be transferred.
8) The first IC sends or receives as many 8-bit words
of data as it wants. After every 8-bit data word the
sending IC expects the receiving IC to
acknowledge the transfer is going OK.
9) When all the data is finished the first chip must
free up the bus and it does that by a special
message called 'STOP'. It is just one bit of
information transferred by a special 'wiggling' of
the SDA/SCL wires of the bus.
Serial Bus Comparison Summary
Pros and Cons of the different buses
UART
CAN
I2 C
• Secure
• Fast
• Fast
• Simple
• Cost effective
• Fast
• Plug&Play HW
• Universally
accepted
• Well known
• Simple
• Low cost
• Low cost
• Universally
accepted
• Large Portfolio
• Plug&Play
• Large portfolio
• Cost effective
• Limited
functionality
• Point to Point
• Complex
• Automotive
oriented
• Limited
portfolio
• Powerful master • No Plug&Play
required
HW
• No Plug&Play
SW - Specific
drivers required
• Limited speed
• No “fixed”
standard
• Expensive
firmware
How are the connected devices
recognized?
DesignCon 2003 TecForum I2C Bus Overview
27
Slide 27
• Master device ‘polls’ used a specific unique identification or
“addresses” that the designer has included in the system
• Devices with Master capability can identify themselves to
other specific Master devices and advise their own specific
address and functionality
Most Philips CAN devices are not plug & play. That is
because for MOST chips the system needs to be fixed
and nothing can be added later. That is because an
added chip is EXPECTED to take part in EVERY data
conversation but will not know the clock speed and
cannot synchronize. That means it falsely reports a bus
timing error on every message and crashes the system.
– Allows designers to build ‘plug and play’ systems
– Bus speed can be different for each device, only a maximum limit
• Only two devices exchange data during one ‘conversation’
DesignCon 2003 TecForum I2C Bus Overview
SPI
• Well Known
• Simple
The bus rules say that when data or addresses are being
sent, the DATA wire is only allowed to be changed in
voltage (so, '1', '0') when the voltage on the clock line is
LOW. The 'start' and 'stop' special messages BREAK
that rule, and that is how they are recognized as special.
USB
Philips has special transceivers that allow them listen to
the bus without taking part in the conversations. This
special feature allows them to synchronize their clocks
and THEN actively join in the conversations. So, from
Philips, it becomes POSSIBLE to do some minor
plug/play on a CAN system.
26
Slide 26
Any device with the ability to initiate messages is
called a ‘master’. It might know exactly what other
chips are connected, in which case it simply addresses
the one it wants, or there might be optional chips and it
then checks what’s there by sending each address and
seeing whether it gets any response (acknowledge).
USB/SPI/MicroWire and mostly UARTS are all just
'one point to one point' data transfer bus systems. USB
then uses multiplexing of the data path and forwarding
of messages to service multiple devices.
An example might be a telephone with a micro in it. In
some models, there could be EEPROM to guarantee
memory data, in some models there might be an LCD
display using an I2C driver. There can be software
written to cover all possibilities. If the micro finds a
display then it drives it, otherwise the program is
arranged to skip that software code. I2C is the simplest
of the buses in this presentation. Only two chips are
involved in any one communication - the Master that
initiates the signals and the one Slave that responded
when addressed.
Only CAN and I2C use SOFTWARE addressing to
determine the participants in a transfer of data between
two (I2C) or more (CAN) chips all connected to the
same bus wires. I2C is the best bus for low speed
maintenance and control applications where devices
may have to be added or removed from the system.
12
AN10216-01 I2C Manual
I2C Theory Of Operation
•
I2C Introduction
•
I2 C
•
•
bus = Inter-IC bus
• Bus developed by Philips in the 80’s
• Simple bi-directional 2-wire bus:
– serial data (SDA)
– serial clock (SCL)
• Has become a worldwide industry standard and used by all
major IC manufacturers
Compatible with a number of processors with
integrated I2C ports (micro 8,16,32 bits) in 8048,
80C51 or 6800 and 68xxx architectures
Easily emulated in software by any microcontroller
Available from an important number of component
manufacturers
I2C Hardware architecture
• Multi-master capable bus with arbitration feature
• Master-Slave communication; Two-device only communication
Pull-up resistors
Typical value 2 kΩ to 10 kΩ
• Each IC on the bus is identified by its own address code
• The slave can be a:
– receiver-only device
– transmitter with the capability to both receive and send data
DesignCon 2003 TecForum I2C Bus Overview
29
SCL
Slide 29
Open Drain structure (or
Open Collector) for both
SCL and SDA
10 pF Max
The I2C bus is a very easy bus to understand and use.
Slides 29 and 30 give a good explanation of bus
specifics and the different speeds. Many people have
asked where rise time is measured and the specification
stipulates it’s between 30% and 70% of VDD. This
becomes important when buffers ‘distort’ the rising
edges on the bus. By keeping any waveform distortions
below 30% of VDD, that portion of the rising edge will
not be counted as part of the formal rise time.
DesignCon 2003 TecForum I2C Bus Overview
Slide 31
I2C Bus Terminology
•
I2C by the numbers
Standard-Mode
Fast-Mode
0 to 100
0 to 400
0 to
1700
0 to
3400
400
400
400
100
1000
300
160
80
Bit Rate
(kbits/s)
Max Cap Load
(pF)
Rise time
(ns)
Spike Filtered
(ns)
Address Bits
High-SpeedMode
N/A
50
10
7 and 10
7 and 10
7 and 10
•
•
Rise Time
•
VDD
VIH
0.7xVDD
VIL
0.3xVDD
•
VOL
0.4 V @ 3 mA Sink Current
GND
DesignCon 2003 TecForum I2C Bus Overview
31
•
30
Slide 30
•
2
I C is a low to medium speed serial bus with an
impressive list of features:
• Resistant to glitches and noise
• Supported by a large and diverse range of
peripheral devices
• A well-known robust protocol
• A long track record in the field
• A respectable communication distance which can
be extended to longer distances with bus extenders
•
•
13
Transmitter - the device that sends data to the bus.
A transmitter can either be a device that puts data
on the bus of its own accord (a ‘mastertransmitter’), or in response to a request from data
from another devices (a ‘slave-transmitter’).
Receiver - the device that receives data from the
bus.
Master - the component that initializes a transfer,
generates the clock signal, and terminates the
transfer. A master can be either a transmitter or a
receiver.
Slave - the device addressed by the master. A slave
can be either receiver or transmitter.
Multi-master - the ability for more than one
master to co-exist on the bus at the same time
without collision or data loss.
Arbitration - the prearranged procedure that
authorizes only one master at a time to take control
of the bus.
Synchronization - the prearranged procedure that
synchronizes the clock signals provided by two or
more masters.
SDA - data signal line (Serial DAta)
SCL - clock signal line (Serial CLock)
AN10216-01 I2C Manual
I2C Address, Basics
START/STOP conditions
µcontroller
• Data on SDA must be stable when SCL is High
I/O
A/D
D/A
LCD
RTC
µcontroller II
SCL
SDA
1010 0 1 1
1010A2A1A0R/W
Fixed Hardware
Selectable
• Each device is addressed individually by software
• Exceptions are the START and STOP conditions
A0
A1
A2
EEPROM
New devices or
functions can be
easily ‘clipped on to
an existing bus!
• Unique address per device: fully fixed or with a programmable part
through hardware pin(s).
S
• Programmable pins mean that several same devices can share the
same bus
P
• Address allocation coordinated by the I2C-bus committee
• 112 different types of devices max with the 7-bit format (others reserved)
DesignCon 2003 TecForum I2C Bus Overview
DesignCon 2003 TecForum I2C Bus Overview
32
33
Slide 32
Slide 33
START and STOP Conditions
Within the procedure of the I2C bus, unique situations
arise which are defined as START (S) and STOP (P)
conditions.
HARDWARE CONFIGURATION
Slide 33 shows the hardware configuration of the I2C
bus. The ‘bus’ wires are named SDA (serial data) and
SCL (serial clock). These two bus wires have the same
configuration. They are pulled-up to the logic ‘high’
level by resistors connected to a single positive supply,
usually +3.3 V or +5 V but designers are now moving
to +2.5 V and towards 1.8 V in the near future.
START: A HIGH to LOW transition on the SDA line
while SCL is HIGH
STOP: A LOW to HIGH transition on the SDA line
while SCL is HIGH
All the connected devices have open-collector (opendrain for CMOS - both terms mean only the lower
transistor is included) driver stages that can transmit
data by pulling the bus low, and high impedance sense
amplifiers that monitor the bus voltage to receive data.
Unless devices are communicating by turning on the
lower transistor to pull the bus low, both bus lines
remain ‘high’. To initiate communication a chip pulls
the SDA line low. It then has the responsibility to drive
the SCL line with clock pulses, until it has finished, and
is called the bus ‘master’.
The master always generates START and STOP
conditions. The bus is considered to be busy after the
START condition. The bus is considered to be free
again a certain time after the STOP condition. The bus
stays busy if a repeated START (Sr) is generated
instead of a STOP condition. In this respect, the
START (S) and repeated START (Sr) conditions are
functionally identical. The S symbol will be used as a
generic term to represent both the START and repeated
START conditions, unless Sr is particularly relevant.
BUS COMMUNICATION
Communication is established and 8-bit bytes are
exchanged, each one being acknowledged using a 9th
data bit generated by the receiving party, until the data
transfer is complete. The bus is made free for use by
other ICs when the ‘master’ releases the SDA line
during a time when SCL is high. Apart from the two
special exceptions of start and stop, no device is
allowed to change the state of the SDA bus line unless
the SCL line is low.
Detection of START and STOP conditions by devices
connected to the bus is easy if they incorporate the
necessary
interfacing
hardware.
However,
microcontrollers with no such interface have to sample
the SDA line at least twice per clock period to sense the
transition.
If two masters try to start a communication at the same
time, arbitration is performed to determine a “winner”
(the master that keeps control of the bus and continue
the transmission) and a “loser” (the master that must
abort its transmission). The two masters can even
generate a few cycles of the clock and data that
‘match’, but eventually one will output a ‘low’ when
the other tries for a ‘high’. The ‘low’ wins, so the
14
AN10216-01 I2C Manual
master releases SDA line to accomplish the
Acknowledge phase. If the other device is connected to
the bus, and has decoded and recognized its ‘address’, it
will acknowledge by pulling the SDA line low. The
responding chip is called the bus ‘slave’.
‘loser’ device withdraws and waits until the bus is freed
again.
There is no minimum clock speed; in fact any device
that has problems to ‘keep up the pace’ is allowed to
‘complain’ by holding the clock line low. Because the
device generating the clock is also monitoring the
voltage on the SCL bus, it immediately ‘knows’ there is
a problem and has to wait until the device releases the
SCL line.
I2C Read and Write Operations (1)
• Write to a Slave device
<
Master
n data bytes >
S
slaveaddress
addressW WA Adata data
S slave
A
A P
A data
data
A P
SCL
transmitter
Slave
receiver
SDA
For full details of the bus capabilities refer to Philips
Semiconductors Specification document ‘The I2C bus
specification’ or ‘The I2C bus from theory to practice’
book by Paret and Fenger published by John Wiley &
Sons.
“0” = Write
Each byte is acknowledged by the slave device
The master is a “MASTER - TRANSMITTER”:
–it transmits both Clock and Data during the all communication
• Read from a Slave device
<
S slave address R
A
SCL
n data bytes >
data
A
data
A
P
receiver
transmitter
SDA
“1” = Read
The I2C specification and other useful application
information can be found on Philips Semiconductors
web site at
http://www.semiconductors.philips.com/i2c/
Each byte is acknowledged by the master device (except the last
one, just before the STOP condition)
The master is a “MASTER TRANSMITTER then MASTER - RECEIVER”:
– it transmits Clock all the time
– it sends slave address data and then becomes a receiver
DesignCon 2003 TecForum I2C Bus Overview
35
Slide 35
I2C Address, 7-bit and 10-bit formats
• The 1st byte after START determines the Slave to be addressed
Terminology for Bus Transfer
• Some exceptions to the rule:
•
– “General Call” address: all devices are addressed : 0000 000 + R/W = 0
– 10-bit slave addressing : 1111 0XX + R/W = X
•
•7-bit addressing
S
X X X X X X X R/W A
The 7 bits
DATA
Only one device will acknowledge
• 10-bit addressing
S
•
1 1 1 1 0 X X R/W A1 X X X X X X X X A2 DATA
XX = the 2 MSBs
The 8 remaining
bits
More than one device can
Only one device will
acknowledge
acknowledge
DesignCon 2003 TecForum I2C Bus Overview
34
•
Slide 34
Slide 34 shows the I2C address scheme. Any I2C device
can be attached to the common I2C bus and they talk
with each other, passing information back and forth.
Each device has a unique 7-bit or 10-bit I2C address.
For 7-bit devices, typically the first four bits are fixed,
the next three bits are set by hardware address pins (A0,
A1, and A2) that allow the user to modify the I2C
address allowing up to eight of the same devices to
operate on the I2C bus. These pins are held high to VCC,
sometimes through a resistor, or held low to GND.
•
The last bit of the initial byte indicates if the master is
going to send (write) or receive (read) data from the
slave. Each transmission sequence must begin with the
start condition and end with the stop condition.
On the 8th clock pulse, SDA is set ‘high’ if data is
going to be read from the other device, or ‘low’ if data
is going to be sent (write). During its 9th clock, the
15
F (FREE) - the bus is free; the data line SDA and
the SCL clock are both in the high state.
S (START) or SR (Repeated START) - data
transfer begins with a start condition (not a start
bit). The level of the SDA data line changes from
high to low, while the SCL clock line remains high.
When this occurs, the bus is ‘busy’.
C (CHANGE) - while the SCL clock line is low,
the data bit to be transferred can be applied to the
SDA data line by a transmitter. During this time,
SDA may change its state, as along as the SCL line
remains low.
D (DATA) - a high or low bit of information on the
SDA data line is valid during the high level of the
SCL clock line. This level must be maintained
stable during the entire time that the clock remains
high to avoid misinterpretation as a Start or Stop
condition.
P (STOP) - data transfer is terminated by a stop
condition, (not a stop bit). This occurs when the
level on the SDA data line passes from the low
state to the high state, while the SCL clock line
remains high. When the data transfer has been
terminated, the bus is free once again.
AN10216-01 I2C Manual
I2C Read and Write Operations (2)
Slide 38 shows how multiple masters can synchronize
their clocks, for example during arbitration. When bus
capacitance affects the bus rise or fall times the master
will also adjust its timing in a similar way.
• Combined Write and Read
<
S slave
slaveaddress
addressW WA
S
A P
“0” = Write
n data bytes >
Adata data
A
<
A data
data
A SrSr slave address R
Each byte is
acknowledged
by the slave device
• Combined Read and Write
<
S slave address R
A
n data bytes >
data
A
data
A
A
m data bytes >
data
A
data
A
P
“1” = Read Each byte is
acknowledged
by the master device
(except the last one, just
before the STOP
condition)
<
I2C Protocol - Arbitration
• Two or more masters may generate a START condition at the same time
• Arbitration is done on SDA while SCL is HIGH - Slaves are not involved
m data bytes >
S
addressW WA AdatadataA
Sr slave
slave address
P
A P
A data
data
A P
“1” = Read
Each byte is
“0” = Write Each byte is
acknowledged
acknowledged
by the master device
by the slave device
(except the last one, just
before the Re-START
condition)
DesignCon 2003 TecForum I2C Bus Overview
Master 1 loses arbitration
DATA1 ≠SDA
36
Slide 36
Slide 36 shows a combined read and write operation.
Start
command
“1”
“0”
“0”
“1”
“0”
“1”
DesignCon 2003 TecForum I2C Bus Overview
39
Acknowledge; Clock Stretching
Slide 39
• Acknowledge
Done on the 9th clock pulse and is mandatory
Æ Transmitter releases the SDA line
Æ Receiver pulls down the SDA line (SCL must be HIGH)
Æ Transfer is aborted if no acknowledge
If there are two masters on the same bus, there are
arbitration procedures applied if both try to take control
of the bus at the same time. When two chips try to start
communication at the same time they may even
generate a few cycles of the clock and data that
‘match’, but eventually one will output a ‘low’ when
the other tries for a ‘high’. The ‘low’ wins, so the
‘loser’ device withdraws and waits until the bus is freed
again. Once a master (e.g., microcontroller) has control,
no other master can take control until the first master
sends a stop condition and places the bus in an idle
state.
No acknowledge
Acknowledge
• Clock Stretching
- Slave device can hold the CLOCK line LOW when performing
other functions
- Master can slow down the clock to accommodate slow slaves
DesignCon 2003 TecForum I2C Bus Overview
37
Slide 37
Slide 37 shows how the Acknowledge phase is done
and how slave devices can stretch the clock signal.
Most Philips slave devices do not control the clock line.
What do I need to drive the I2C bus?
Slave 1
Slave 2
Slave 3
Slave 4
Master
I2C BUS
I2C
Protocol - Clock Synchronization
Vdd
Master 1
CLK 1
SCL
There are 3 basic ways to drive the I2C bus:
1) With a Microcontroller with on-chip I2C Interface
Bit oriented - CPU is interrupted after every bit transmission
(Example: 87LPC76x)
Byte oriented - CPU can be interrupted after every byte transmission
(Example: 87C552)
Master 2
CLK 2
2) With ANY microcontroller: 'Bit Banging’
The I2C protocol can be emulated bit by bit via any bi-directional open drain port
3) With a microcontroller in conjunction with bus controller like the
PCF8584 or PCA9564 parallel to I2C bus interface IC
1
4
2
DesignCon 2003 TecForum I2C Bus Overview
40
3
Slide 40
• LOW period determined by the longest clock LOW period
Slide 40 shows there are multiple ways to control I2C
slaves.
• HIGH period determined by shortest clock HIGH period
DesignCon 2003 TecForum I2C Bus Overview
38
Slide 38
16
AN10216-01 I2C Manual
•
Pull-up Resistor calculation
DC Approach - Static Load
Worst Case scenario: maximum current load that the output transistor can
handle Æ 3 mA . This gives us the minimum pull-up resistor value
Vdd min - 0.4 V
R=
With Vdd = 5V (min 4.5 V), Rmin = 1.3 kΩ
3 mA
The I2C bus is a de facto world standard that is
implemented in over 1000 different ICs (Philips
has > 400) and licensed to more than 70 companies
I2C Bus recovery
• Typical case is when masters fails when doing a read operation in a slave
AC Approach - Dynamic load
• SDA line is then non usable anymore because of the “Slave-Transmitter”
mode.
• maximum value of the rise time:
• Methods to recover the SDA line are:
– 1µs for Standard-mode (100 kHz)
– 0.3 µs for Fast-mode (400 kHz)
– Reset the slave device (assuming the device has a Reset pin)
• Dynamic load is defined by:
– Use a bus recovery sequence to leave the “Slave-Transmitter” mode
– device output capacitances
(number of devices)
– trace, wiring
DesignCon 2003 TecForum I2C Bus Overview
V(t) = VDD (1-e -t /RC )
Rising time defined between
30% and 70%
• Bus recovery sequence is done as following:
1 - Send 9 clock pulses on SCL line
2 - Ask the master to keep SDA High until the “Slave-Transmitter” releases
the SDA line to perform the ACK operation
Trise = 0.847.RC
41
3 - Keeping SDA High during the ACK means that the “Master-Receiver”
does not acknowledge the previous byte receive
Slide 41
4 - The “Slave-Transmitter” then goes in an idle state
5 - The master then sends a STOP command initializing completely the
bus
Slide 41 shows the typical resistor values needed for
proper operation. C is the total capacitance on either
SDA or SCL bus wire, with R as its pull-up resistor.
DesignCon 2003 TecForum I2C Bus Overview
Slide 42
I2C Designer Benefits
•
•
•
•
•
•
•
•
42
Slide 42 shows how a hung bus could be recovered.
The bus can become hung for several reasons, e.g.….
1. Incorrect power-up and/or reset procedure for
ICs
2. Power to a chip is interrupted – brown-outs etc
3. Noise on the wiring causes false clock or data
signals
Functional blocks on the block diagram correspond
with the actual ICs; designs proceed rapidly from
block diagram to final schematic.
No need to design bus interfaces because the I2C
bus interface is already integrated on-chip.
Integrated addressing and data-transfer protocol
allow systems to be completely software-defined.
The same IC types can often be used in many
different applications.
Design-time reduces as designers quickly become
familiar with the frequently used functional blocks
represented by I2C bus compatible ICs.
ICs can be added to or removed from a system
without affecting any other circuits on the bus.
Fault diagnosis and debugging are simple;
malfunctions can be immediately traced.
Assembling a library of reusable software modules
can reduce software development time.
I2C Protocol Summary
START
STOP
DATA
ACKNOWLEDGE
CLOCK
ARBITRATION
HIGH to LOW transition on SDA while SCL is HIGH
LOW to HIGH transition on SDA while SCL is HIGH
8-bit word, MSB first (Address, Control, Data)
- must be stable when SCL is HIGH
- can change only when SCL is LOW
- number of bytes transmitted is unrestricted
- done on each 9th clock pulse during the HIGH period
- the transmitter releases the bus - SDA HIGH
- the receiver pulls DOWN the bus line - SDA LOW
- Generated by the master(s)
- Maxim um speed specified but NO minimum speed
- A receiver can hold SCL LOW when performing
another function (transmitter in a Wait state)
- A master can slow down the clock for slow devices
- Master can start a transfer only if the bus is free
- Several masters can start a transfer at the same time
- Arbitration is done on SDA line
- Master that lost the arbitration must stop sending data
I2C Manufacturers Benefits
•
•
•
•
The simple 2-wire serial I2C bus minimizes
interconnections so ICs have fewer pins and there
are not so many PCB tracks; result - smaller and
less expensive PCBs
The completely integrated I2C bus protocol
eliminates the need for address decoders and other
‘glue logic’
The multi-master capability of the I2C bus allows
rapid testing/alignment of end-user equipment via
external connections to an assembly-line
Increases system design flexibility by allowing
simple construction of equipment variants and easy
upgrading to keep design up-to-date
DesignCon 2003 TecForum I2C Bus Overview
Slide 43
Slide 43 provides a summary of the I2C protocol.
17
43
AN10216-01 I2C Manual
I2C Summary - Advantages
For example, in an application where 4 identical I2C
EEPROMs are used (EE1, EE2, EE3 and EE4), a four
channel PCA9546 can be used. The master is plugged
to the main upstream bus while the 4 EEPROMs are
plugged to the 4 downstream channels (CH1, CH2,
CH3 and CH4). If the master needs to perform an
operation on EE3, it will have to:
- Connect the upstream channel to CH3
- Simply communicate with EE3.
• Simple Hardware standard
• Simple protocol standard
• Easy to add / remove functions or devices (hardware and software)
• Easy to upgrade applications
• Simpler PCB: Only 2 traces required to communicate between devices
• Very convenient for monitoring applications
• Fast enough for all “Human Interfaces” applications
– Displays, Switches, Keyboards
– Control, Alarm systems
EE1, EE2 and EE4 are electrically removed from the
main I2C bus as long as CH3 is selected. Some of the
I2C multiplexers offer an Interrupt feature, allowing
collection of the different downstream Interrupts
(generated by the downstream devices). An Interrupt
output provides the information (transition from High
to Low) to the master every time one or more Interrupt
is generated (transition from High to Low) by any of
the downstream devices.
• Large number of different I2C devices in the semiconductors business
• Well known and robust bus
DesignCon 2003 TecForum I2C Bus Overview
44
Slide 44
Slide 44 summarizes the advantages of the I2C bus.
Overcoming Previous Limitations
I2C Multiplexers: Address Deconflict
Address Conflicts
How to solve I2C address conflicts?
I2C EEPROM
1
• I2C protocol limitation: when a device does not have its I2C address
programmable (fixed), only one same device can be plugged in the same
bus
Î An
I2 C
I2C EEPROM
2
MASTER
Same I2C devices with same address
multiplexer can be used to get rid of this limitation
I2C EEPROM
1
• It allows to split dynamically the main I2C in several sub-branches in order to
talk to one device at a time
• It is programmable through I2C so no additional pins are required for control
• More than one multiplexer can be plugged in the same I2C bus
I2C MULTIPLEXER
MASTER
The multiplexer allows to address 1 device
then the other one
• Products
# of Channels
2
4
8
I2C EEPROM
2
Standard
PCA9540
PCA9546
PCA9548
w/Interrupt Logic
PCA9542/43
PCA9544/45
DesignCon 2003 TecForum I2C Bus Overview
DesignCon 2003 TecForum I2C Bus Overview
48
Slide 48
47
The SCL/SDA upstream channel fans out to multiple
SCx/SDx channels that are selected by the
programmable control register. The I²C command is
sent via the main I²C bus and is used to select or
deselect the downstream channels.
Slide 47
A 7 or 10-bit address that is unique to each device
identifies an I2C device.
This address can be:
• Partly fixed, part programmable (allowing to have
more than one of the same device on the same bus)
• Fully fixed allowing to have only one single same
device on the device.
The Multiplexers can select none or only one SCx/SDx
channels at a time since they were designed primarily
for address conflict resolution such as when multiple
devices with the same I2C address need to be attached
to the same I2C bus and you can only talk to one of the
devices at a time.
If more than one same “non programmable” device
(fully fixed address) is required in a specific
application, it is then necessary to temporarily remove
the non-addressed device(s) from the bus when talking
with the targeted device. I2C multiplexers allow to
dynamically split the main I2C bus into 2, 4 or 8 subI2C buses. Each sub-bus (downstream channel) can be
connected to the main bus (upstream channel) by a
simple 2-byte I2C command.
These devices are used in video projectors and server
applications. Other applications include:
• Address conflict resolution (e.g., SPD EEPROMs
on DIMMs).
• I2C sub-branch isolation
18
AN10216-01 I2C Manual
•
I2C bus level shifting (e.g., each individual
SCx/SDx channel can be operated at 1.8 V, 2.5 V,
3.3 V or 5.0 V if the device is powered at 2.5 V).
Multiplexers allow dynamic splitting of the overloaded
I2C bus into several sub-branches with a total capacitive
load smaller than the specified 400 pF. Note that this
method does not allow the master to access all the buses
at the same time. Only part of the bus will be accessible
at a time.
Interrupt logic inputs for each channel and a combined
output are included on every multiplexer and provide a
flag to the master for system monitoring. These devices
do not isolate the capacitive loading on either side of
the device so the designer must take into account all
trace and device capacitance on both sides of the device
and on any active channels. Pull up resistors must be
used on all channels
Multiplexers allow bus splitting but do not have a
buffering capability. Buffers and repeaters allow
increasing the total capacitive load beyond the 400 pF
without splitting the bus in several branches. If a
PCA9515 is used, the bus can be loaded up to 800 pF
with 400 pF on each side of the device.
Capacitive Loading > 400 pF (isolation)
How to go beyond I2C max cap load?
Practical case: Multi-card application
• I2C protocol limitation: the maximum capacitive load in a bus is 400 pF. If the
load is higher AC parameters will be violated.
• The following example shows how to build an application where:
– Four identical control cards are used (same devices, same I2Caddress)
– Devices in each card are controlled through I2C
– Each card monitors and controls some digital information
– Digital information is:
1) Interrupt signals (Alarm monitoring)
2) Reset signals (device initialization, Alarm Reset)
– Each card generates an Interrupt when one (or more) device generates
an Interrupt (Alarm condition detected)
– The master can handle only one Interrupt signal for all the application
Î An I2C multiplexer can be used to get rid of this limitation
• It allows to split dynamically the main I2C in several sub-branches in order to
divide the bus capacitive load
• It is programmable through I2C so no additional pins are required for control
• More than one multiplexer can be plugged in the same I2C bus
• LIMITATION: All the sub-branches cannot be addressed at the same time
• Products:
# of Channels
2
4
8
Standard
PCA9540
PCA9546
PCA9548
w/Interrupt Logic
PCA9542/43
PCA9544/45
DesignCon 2003 TecForum I2C Bus Overview
DesignCon 2003 TecForum I2C Bus Overview
49
51
Slide 49
Slide 51
The I2C specification limits the maximum capacitive
load in the bus to 400 pF. In applications where a
higher capacitive load is required, 2 types of devices
can be used:
• I2C multiplexers and switches
• I2C buffers and repeaters
In this application, 4 identical cards are used. Identical
means that the same devices are used, and that the I2C
devices on each card have the same address. Each card
monitors and controls some specific signal and those
signals are controlled/monitored through the I2C bus by
using a PCA9554 type device.
In this application, each card monitors some alarm
system’s sub system and controls some LEDs for visual
status. Each alarm, when triggered, generates an
Interrupt that is sent to the master for processing.
PCA9554 collects the Interrupt signals and sends a
“Card General Interrupt” to the master. When the
master processes the alarm, it sends a Reset signal to
the corresponding alarm to clear it. Master receives
only an Interrupt signal, which is a combination of all
the Interrupt signals in the cards. Since the cards are
identical, it is then necessary to deconflict the different
addresses and isolate the cards that are not accessed.
I2C Multiplexers: Capacitive load split
500 pF
MASTER
I2C bus
200 pF
I2C bus 2
200 pF
I2C bus 3
300 pF
I2C MULTIPLEXER
MASTER
300 pF
I2C bus 1
100 pF
The multiplexer splits the bus in two downstream 200
pF busses + 100 pF upstream
DesignCon 2003 TecForum I2C Bus Overview
PCA9544 in this application has 2 functions:
• Deconflict the I2C addresses by creating 4 sub I2C
busses that can be isolated
• Collect the Interrupt from each card and propagate
a “General Interrupt” to the master
50
Slide 50
19
AN10216-01 I2C Manual
high level voltage value, determined by the voltage
applied to the pull up resistors. In applications where
several voltage levels are required (e.g. accommodate
legacy architecture at 5.0 V with newer devices
working at 3.3 V only), I2C switches allow creating a
bus with different high level voltage values at a
minimum cost.
I2C Multiplexers: Multi-card Application
- Cards are identical
- One card is selected / controlled
at a time
- PCA9544 collects Interrupt
Card 0
Card 1
Card 2
Card 3
0
I2C
PCA
9544
bus 0
I2C bus 1
I2C
INT0
Reset
Reset
Alarm 1
Alarm 1
bus 2
I2C bus 3
MASTER
INT
1
1
INT1
INT2
1
INT3
In this example, we have an existing 5.0 V I2C bus and
we want to add some new features with devices “non
5.0 V tolerant”. An I2C bus can be used. The master
controlling the existing and new devices will be located
in the upstream channel and the 2 downstream channels
will be used with pull up resistors at 5.0 V in one and to
3.3 V in the other one. Software changes will include
the drivers for the new 3.3 V devices and a simple 2byte command allows to program the I2C switch with
the 2 downstream channels active all the time. The
master then sees an I2C bus with new devices and does
not have to take care of the high level voltage required
to make them work correctly. It does not have to care
either about the location of the device it needs to talk to
(downstream channel 0 or channel 1) since both are
active at the same time.
Int
PCA 0
95540
Int
Reset
Sub
System
Int
INT
Interrupt signals are
collected into one signal
DesignCon 2003 TecForum I2C Bus Overview
52
Slide 52
When one card in the application triggers an alarm
condition, the PCA9554 collects it through one of its
inputs and generates an Interrupt (at the card level).
PCA9544 collects the Interrupts (from each card) and
sends a “General Interrupt” to the master.
1. Master then interrogates the PCA9544 Interrupt
status register in order to determine which card is
in cause
2. Master then connects the corresponding sub I2C
channel in order to interrogate the PCA9554 by
reading its Input register.
3. Once 1) and 2) are done, Master knows which
alarm has been triggered and can process it
When this is done, Master can then clear the
corresponding alarm by accessing the corresponding
card and programming the PCA9554 (write in the
output register)
I2C Switches: Voltage Level Shifting
I2C device I2C device I2C device I2C device I2C device
1
2
3
4
5
Devices supplied by 5V
MASTER
I2C bus
• Products
# Channels
1
I2C device I2C device I2C device
1
2
3
2
4
MASTER
Voltage Level Translation
How to accommodate different I2C logic
levels in the same bus?
I2C
SWITCH
I2C
device
4
I2C
device
5
5V bus
Int
GTL2002
PCA9540
PCA9542/43
X
PCA9546
PCA9544/45
X
5
GTL2010
8
11
PCA9548
GTL2000
3.3V bus
DesignCon 2003 TecForum I2C Bus Overview
• I2C protocol: Due to the open drain structure of the bus, voltage level in the
bus is fixed by the voltage connected to the pull-up resistor. If different
voltage levels are required (e.g., master core at 1.8 V, legacy I2C bus at 5 V
and new devices at 3.3 V), voltage level translators need to be used
54
Slide 54
The SCL/SDA upstream channel fans out to multiple
SCx/SDx channels that are selected by the
programmable control register. The Switches can select
individual SCx/SDx channels one at a time, all at once
or in any combination through I2C commands and very
primary designed for sub-branch isolation and level
shifting but also work fine for address conflict
resolution. Just make sure you do not select two
channels at the same time.
Î An I2C switch can be used to accommodate those
different voltage levels.
• It allows to split dynamically the main I2C in several sub-branches and allow
different supply voltages to be connected to the pull up resistors
• PCA devices are programmable through I2C bus so no additional pin is
required to control which channel is active
• More than one channel can be active at the same time so the master does
not have to remember which branch it has to address (broadcast)
• More than one switch can be plugged in the same I2C bus
DesignCon 2003 TecForum I2C Bus Overview
Devices supplied by 3.3V
and not 5.0 V tolerant
53
Applications are the same as for the multiplexers but
since multiple channels can be selected at the same time
the switches are really great for I2C bus level shifting
(e.g., individual SCx/SDx channels at 1.8 V, 2.5 V, 3.3
V or 5.0 V if the device is powered at 2.5 V). A
Slide 53
Due to the open drain architecture of the I2C bus, pull
up resistors to a specific voltage is required. Once this
is done, all the devices in the bus will have the same
20
AN10216-01 I2C Manual
hardware reset pin has been added to all the switches. It
provides a means of resetting the bus should it hang up,
without rebooting the entire system and is very useful
in server applications where it is impractical to reset the
entire system when the I2C bus hangs up. The switches
reset to no channels selected.
Isolate I2C hanging segment(s)
Device 1
Device 2
MASTER
PCA
9548
Device 3
Device 4
Interrupt logic inputs and output are available on the
PCA9543 and PCA9545 and provide a flag to the
master for system monitoring. The PCA9546 is a lower
cost version of the PCA9545 without Interrupt Logic.
The PCA9548 provides eight channels and are more
convenient to use then dual 4 channel devices since the
device address does not have to shift.
Device 5
RESET
Device 6
Device 7
Device 8
DesignCon 2003 TecForum I2C Bus Overview
These devices do not isolate the capacitive loading on
either side of the device so the designer must take into
account all trace and device capacitance on both sides
of the device (active channels only). Pull up resistors
must be used on all channels.
Slide 56
Let’s take an example where 8 devices (DEV1 to
DEV8) are used and where the functional devices need
to be controlled even though one or more devices are
failing.
Increase I2C Bus Reliability (Slave Devices)
How to increase reliability of an I2C bus?
(Slave devices)
Slave devices will be located on each downstream
channel of the PCA9548 (8-channel switch with Reset)
(CH1 to CH8). At power up, all the downstream
channels are disabled. The master (located in the
upstream channel) sends a 2 byte command enabling all
the downstream channels. The I2C bus is then a normal
bus with a master and 8 slave devices. Let’s assume
that DEV4 (in CH4) fails. The bus then hangs and
cannot be normally controlled by the master anymore.
• I2C protocol: If one device does not work properly and hangs the bus, then
no device can be addressed anymore until the rogue device is separated from
the bus or reset.
Î An I2C switch can be used to split the I2C bus in several
branches that can be isolated if the bus hangs up.
• Switches allow the main I2C to be split dynamically in several sub-branches
that can be:
– active all the time
– deactivated if one device of a particular branch hangs the bus
• When a malfunctioning sub-branch has been isolated, the other sub
branches are still available
• It is programmable through I2C so no additional pin is required to control it
• More than one switch can be plugged in the same I2C bus
DesignCon 2003 TecForum I2C Bus Overview
56
After detection of this condition, the master must go to
a maintenance routine where:
• It resets the PCA9548, thus disabling all the
downstream channels.
• It enables one by one all the downstream channels
(CH1 to CH8) until the bus hangs again (CH4
active).
The master then knows that the device connected to
CH4 is responsible of the failure
• It resets again the PCA9548 to take control of the
I2C bus
• It programs all the functional channels active (CH1
to 3, CH5 to 8) and disables CH4
55
Slide 55
Due to the open drain architecture of the I2C bus, if a
device fails in the bus and keeps the clock or data line
at a high or low level, the bus is stuck in this
configuration and no device can be controlled until the
failed device is isolated from the I2C bus. Some
architectures require a bus to still be operational even
though one or more devices failed and can no longer
operate normally.
Note that this algorithm can also be applied if more
than 1 channel hang the bus at the same time.
An I2C switch with a Reset capability allows to:
• Split dynamically the I2C bus in several subbranches (with one or several devices on each)
• Disconnect all the devices in case the bus hangs
• Reprogram the bus and isolate one or more branch
that is not working properly.
21
AN10216-01 I2C Manual
Isolate hanging segments
Discrete stand alone solution
P82
Isolate failing master
Slave
MAIN
MASTER
SEGMENT 1
B96
MASTER
P82
SDA
Demux
SCL
BACKUP
MASTER
SEGMENT 2
B96
P82
I22C
Slave
• Main Master control the
SEGMENT 3
B96
Main
I2 C
bus
I2 C
bus
• When it fails, backup master asks to take control of the bus
• Previous master is then isolated by the multiplexer
• A bus buffer isolates the branch (capacitive isolation)
• Its power supply is controlled by a bus sensor
• SDA and SCL are sensed and the sensor generates a timeout when the
bus stays low
• Downstream bus is initialized (all devices waiting for START condition)
• Switch to the new master is done
• Products
Device
PCA9541
• Bus buffer is Hi-Z when power supply is off.
DesignCon 2003 TecForum I2C Bus Overview
# of upstream channels
2
DesignCon 2003 TecForum I2C Bus Overview
57
59
Slide 57
Slide 59
Slide 57 shows one discrete solution with option to set
timing, by discrete capacitors, to isolate a bus segment.
The 2:1 master selector allows switching between one
master and its backup (and vice versa if the main master
comes back on line). Before switching from one
upstream channel to the other one, the device makes
sure that the previous device is not on the bus anymore
(fully isolated)
Increasing I2C Bus Reliability (Master Devices)
How to increase reliability of an I2C bus?
(Master devices)
The switching is done after making sure that the
downstream bus is in a “clean” configuration. All the
downstream devices have been initialized again
(essential when the previous master failed in the middle
of a transaction and thus the bus is not well initialized)
and the bus is in an idle configuration. This is done by
converting the 2:1 master selector into a temporary
master (just after isolating the failing master) allowing
it to send the necessary I2C sequence (9 clock pulses on
SCL while SDA is maintained high then a STOP
command). While the sequence is done, the
downstream I2C bus is well initialized and the switch to
the new master can be performed automatically by the
PCA9541.
• I2C protocol: If the master does not work properly , reliability of the systems
will decrease since monitoring or control of critical parameters are not
possible anymore (voltage, temperature, cooling system)
Î An I2C demultiplexer can be used to switch from one
failing master to its backup.
• It allows to have 2 independent masters to control the bus without any fault
or system corruption
– failed master completely isolated from the bus
– I2C bus is initialized by the demultiplexer before switching from one
master to the other one
• It is programmable through I2C so no additional pin is required to control it
• More than one demultiplexer can be plugged in the same I2C bus
DesignCon 2003 TecForum I2C Bus Overview
58
Slide 58
If the I2C master fails or does not work properly,
reliability of applications will decrease since
monitoring and control of essential parameters cannot
be controlled anymore (e.g. temperature monitoring,
voltage monitoring, cooling control). It is then often
essential to have a backup I2C master to replace a mal
functioning main I2C master. The I2C 2:1 master
selector is then an essential device allowing switching
between 2 masters.
Capacitive Loading > 400 pF (Buffer)
How to go beyond I2C max cap load?
• I2C protocol limitation: the maximum capacitive load in a bus is 400 pF. If the
load is higher AC parameters will be violated.
Î An I2C bus repeater or an I2C hub can be used to get rid
of this limitation
• It allows to double the I2C max capacitive load (repeater) or to make it 5
times higher (hub = 5 repeaters)
• Multi-master capable, voltage level translation
• All channels can be active at the same time
• Limitation: Repeater/hub cannot be used in series
It can be used in:
• A point to point application - master and backup
master control one card
• A multi point application - master and backup
master control several cards.
• Products:
Device
PCA9515
PC9516
# of repea te rs
1
5
# of ENABLE pins
1
4
DesignCon 2003 TecForum I2C Bus Overview
Slide 60
22
60
AN10216-01 I2C Manual
I2C bus repeaters and hubs allow increasing the
maximum capacitive load on the bus without degrading
the AC performances (rising and falling times) of the
data and clock signals. They are multi-master capable.
Using the PCA9516 in this application, the sub masters
can only talk with sub masters on the same hub or the
main master since a low signal can not be sent through
two hubs. Sub masters will not be able to arbitrate for
bus control if located on different hubs. That is not
ideal and limits the designers’ ability to expand their
I2C bus. The PCA9515 and the PCA9516 can only be
used one device (either the PCA9515 or PCA9516) per
system since low levels will not be transmitted through
the second device.
I2C Bus repeater (PCA9515) and Hub (PCA9516)
Master
PCA
9515
Hub
Hub 11
To overcome this limitation, the PCA9518 was
released. Similar to the PCA9516 but with four extra
open drain signal pins that allow the internal device
logic to be interconnected into an unlimited number of
segments with only one repeater delay between any two
segments.
Hub 2
Hub
Hub 33
PCA
9516
Hub 4
Hub
Hub 55
DesignCon 2003 TecForum I2C Bus Overview
PCA9518 Applications
61
•
•
Hub 2
Hub 5
Master
Master
I2 C
Inter Device I2C bus
Hub 12
Non used Hub
PCA
9518
Hub 11
Hub 10
PCA
9518
DesignCon 2003 TecForum
Hub 15
Hub 14
Hub
Hub 99
Hub 13
I2C
Bus Overview
63
Slide 63
How to scale the I2C bus by adding
400 pF segments?
The PCA9518, like the PCA9515/16, is transparent to
bus arbitration and contention protocols in a multimaster environment and any master can talk to any
other master on any segment. The enable pins can be
used to isolate four of the five segments per device.
Place a pull up resistor on the un-isolatable segment
and leave it unused if there is a requirement to enable or
disable the segment.
• Some applications require architecture enhancements where one or several
isolated I2C hubs need to be added with the capability of hub to hub
communication
Î An expandable I2C hub can be used to easily upgrade
this type of application
• It allows to expand the numbers of hubs without any limit
• Multi-master capable, voltage level translation
• All channels can be active at the same time (4 channels per expandable hub
can be individually disabled)
Using the PCA9518 in this 15 hub application, any sub
master can talk to any other sub master on any of the
cards and the main master can talk with any sub master
with only one repeater delay.
• Products:
# of ENABLE pins
4
DesignCon 2003 TecForum I2C Bus Overview
Hub 7
Hub 6
Hub 1
In Slide 61, the possible communication paths are
shown in green. No communication is possible over the
red paths, no hub can communicate with any other hub.
When communication between all hubs and the master
is required then a multi-drop bus approach with P82B96
should be used.
# of repeate rs
5
PCA
9518
PCA
9518
Hub 3
Repeaters allow doubling the capacitive load, 400
pF on each side of the device
Hubs allow multiplying the load by 5 with 400 pF
on each hub channel
Device
PCA9518
Hub 8
Hub 4
Slide 61
62
Slide 62
There are some applications where more than 5
channels are required. Sub Masters on Server Blades
Application - Main Master is able to isolate any blade
with the hardware enable pin via I2C & GPIO
23
AN10216-01 I2C Manual
•
How to accommodate 100 kHz and 400 kHz
devices in the same I2C bus?
• I2C protocol limitation: in an application where 100 kHz and 400 kHz devices
(masters and/or slaves) are present in the same bus, the lowest frequency
must be used to guarantee a safe behavior.
•
Î An I2C bus repeater can be used to isolate 100 kHz from
400 kHz devices when a 400 kHz communication is
required
In the 1st case, the master located in the “400 kHz only”
side has the capability to control the PCA9515’s
ENABLE pin in order to disable the device when a 400
kHz communication is initiated (the “100 kHz only”
side will then not see the communication). During a 100
kHz communication, the PCA9515 is enabled to allow
communication with the other side. In the 2nd case, both
masters are located in each side of the PCA9515 and
the control is basically the same as above for the 400
kHz devices.
• It allows to easily upgrade applications where legacy 100 kHz I2C devices
share bus access with newer 400 kHz I2C devices
• Each side of the repeater can work with different logic voltage levels
• Products:
Device
PCA9515
# of repeaters
1
# of ENABLE pins
1
DesignCon 2003 TecForum I2C Bus Overview
One main master with the ability of choosing
between 100 kHz and 400 kHz depending on the
devices it needs to talk to.
Two masters, one working at 100 kHz only (can be
part of the system legacy) and another one working
at 400 kHz.
64
Slide 64
Due to the different I2C specification available (100
kHz, 400 kHz and now 3.4 MHz), devices designed for
the 100 kHz specification are not suitable to work
properly at 400 kHz, while the opposite is true. In
applications where upgrades have been performed by
using newer 400 kHz devices while keeping the 100
kHz legacy devices, it may become necessary to
separate the 400 kHz devices from the 100 kHz devices
when a 400 kHz I2C transfer is performed.
Live Insertion into the I2C Bus
How to live insert?
I2C
•
protocol limitation: in an application where the I2C bus is active, it was
not designed for insertion of new devices.
Î An I2C hot swap bus buffer can be used to detect bus idle
condition isolate capacitance, and prevent glitching SDA &
SCL when inserting new cards into an active backplane.
• Repeaters work with the same logic level on each side except the PCA9512
which works with 3.3 V and 5 V logic voltage levels at the same time
PCA9515 - Application Example
• Products:
400 kHz slave
devices
3.3 V
Device
PCA9511
PCA9512
PCA9513
PCA9514
5.0 V
SCL0
SCL1
SDA0
SDA1
100 kHz slave
devices
# of repeaters
1
1
1
1
# of ENABLE pins
1
0
1
1
DesignCon 2003 TecForum I2C Bus Overview
ENABLE
MASTER 1
400 kHz
OPTIONAL
MASTER 2
100 kHz
Slide 66
• Master 1 works at 400 kHz and can access 100 & 400 kHz slaves at their
maximum speed (100 kHz only for 100 kHz devices)
The I2C bus was never designed to be used in live
insertion applications, but newer applications in for
telecom cards that require 24/7 operation require the
ability to be removed and inserted into an active system
for maintenance and control applications.
• Master 2 works at only 100 kHz
• PCA9515 is disabled (ENABLE = 0) when Master 1 sends commands at
400 kHz
DesignCon 2003 TecForum I2C Bus Overview
66
65
Slide 65
The PCA9515 can be used for this purpose. One side of
the device will have all the devices running at 400 kHz
while the other side will have all the devices running to
100 kHz.
Note that each side of the PCA9515 can work at
different logic voltage levels. For example, the “older”
100 kHz devices can run at 5.0 V while the “newer”
400 kHz devices can work at 3.3 V.
There could also be more than one master in the bus:
24
AN10216-01 I2C Manual
Parallel to I2C Bus Controller
I2C Hot Swap Bus Buffer
How to use a micro-controller without I2C bus or
how to develop a dual master application with a
single micro-controller?
PLUG
SCL0
SCL1
SDA0
SDA1
• Some micro-controllers integrates an I2C port, others don’t
READY
Î An I2C bus controller can be used to interface with the
micro-controller’s parallel port
• Card is plugged on the system - Buffer is on Hi-Z state
• It generates the I2C commands with the instructions from the micro
controller’s parallel port (8-bits)
• It receives the I2C data from the bus and send them to the micro-controller
• It converts by software any device with a parallel port to an I2C device
• Bus buffer checks the activity on the main I2C bus
• When the bus is idle, upstream and downstream buses are connected
• Ready signal informs that both buses are connected together
DesignCon 2003 TecForum I2C Bus Overview
67
DesignCon 2003 TecForum I2C Bus Overview
69
Slide 67
Slide 69
The PCA9511/12/13/14 are designed for these types of
live insertion applications.
There are many applications where there is a need to
convert 8 bits of parallel data into an I2C bus port. The
PCF8584 and PCA9564 allow building a single I2C
master system using the parallel port of a 8051 type
microcontroller that does not have an I2C interface. It
also allows building a double master system with using
the built-in I2C interface and the parallel port of the
same micro-controller.
Long I2C Bus Lengths
How to send I2C commands through long cables?
• I2C limitation: due to the bus 400 pF maximum capacitive load limit, sending
commands over wire (80 pF/m) long distances is hard to achieve
Î An I2C bus extender can be used
• It has high drive outputs
• Possible distances range from 50 meters at 85 kHz to 1km at 31 kHz over
twisted-pair phone cables. Up to 400 kHz over short distances.
Parallel Bus to I2C Bus Controller
• Others applications:
– Multi-point applications: link applications, factory applications
– I2C opto-electrical isolation
– Infra-red or radio links
• Master without I2C interface
Master
• Products:
Device
P82B715
P82B96
SDA
SCL
PCA
9564
• Multi-Master capability or 2 isolated I2C bus with the same device
DesignCon 2003 TecForum I2C Bus Overview
68
Master
SDA1
SCL1
SDA2
SCL2
PCA
9564
Slide 68
• Products
Voltage range
PCF8584
4.5 - 5.5V
PCA9564 2.3 - 3.6V w/5V tolerance
The P82B715 and P82B96 are designed for long
distance transmission of the I2C bus.
Max I2C freq
90 kHz
360 kHz
DesignCon 2003 TecForum I2C Bus Overview
Clock source
External
Internal
Parallel interface
Slow
Fast
70
Slide 70
Philips offers two devices, the PCF8584 and PCA9564.
The PCA9564 is similar to the PCF8584 but operates at
2.3 to 3.6 V VCC and up to 360 kHz with various
enhancements added that were requested by engineers.
The PCA9564 serves as an interface between most
standard parallel-bus microcontrollers/ microprocessors
and the serial I2C bus and allows the parallel bus system
to communicate bi-directionally with the I2C bus. This
commonly is referred as the bus master.
Communication with the I2C bus is carried out on a
byte-wise basis using interrupt or polled handshake. It
25
AN10216-01 I2C Manual
controls all the I2C bus specific sequences, protocol,
arbitration and timing. The internal oscillator in the
PCA9564 is regulated to within +/- 10%.
1. Voltage range
2. Max I2C freq.
3. Clock source
flexible
4. Parallel interface
processors
WIN-I2CNTDLL: 32-bit Win-I2CNT kit including
DLL driver and docs - Developer Kit for 32-bit
embedded I2C applications
PCA9564
2.3-3.6V
360 kHz
Internal
PCF8584
4.5-5.5V
90 kHz
External
Comments
PCA9564 is 5V tolerant
Faster I2C
Less expensive and more
WIN-I2CNT: 32-bit I2C Software/Adapter kit for Win
95/98/ME/2000, NT 4.x - Enhanced kit for I2C control.
Free updates from the Website
Fast
Slow
Compatible with faster
WIN-I2C: General Purpose legacy 16-bit I2C
Software/Adapter kit - Basic Legacy Kit for I2C control
with PCs running Windows 3.1x
In addition, the PCA9564 has been made very similar to
the Philips standard 80C51 microcontroller I2C
hardware so existing code can be utilized with a few
modifications.
I2CPORT: General Purpose I2C LPT Printer Port
Adapter v1.0 - Generic I2C adapter (Not compatible
with Win-I2C/Win-I2CNT Software)
Development Tools and Evaluation Board
Overview
Evaluation Board 2002-1 Kit Overview
2
Purpose of the Development Tool and I C
Evaluation Board
CD - ROM
PC -Win95/98/2000/NT/XP
Parallel
Port
Win-I2CNT
Win-I2CNT
Software
Software
To provide a low cost platform that allows Field
Application Engineers, designers and educators to
easily test and demonstrate I2C devices in a platform
that allows multiple operations to be performed in a
setting similar to a real system environment.
I2C 2002-1
Evaluation Kit
I2CPORT
v2 Port
I2CPORT
v2
Adapter Card
Port Adapter
Card
I2C Cable
USB
Adapter
Card
I2C Cable
USB
Cable
9V
Power
Supply
I2C 2002-1 Evaluation Board(s)
9V
Power
Supply
I2C 2002-1 Evaluation Board(s)
I2C Cable
USB Cable
DesignCon 2003 TecForum I2C Bus Overview
I2C 2002-1A Evaluation Board Kit
74
Slide 74
Slide 74 shows how the I2C 2002-1A kit is connected
and shows how two evaluation boards can be used at
the same time.
I2CPORT v2 Adapter Card
FEATURES
- Converts Personal Computer parallel port to I2C bus master
- Simple to use graphical interface for I2C commands
- Win-I2CNT software compatible with Windows 95, 98, ME, NT, XP and 2000
- Order kits at www.demoboard.com
DesignCon 2003 TecForum I2C Bus Overview
• The Win-I2CNT adapter connects to the standard DB-25 on any PC
• It can be powered by the PC or by the evaluation board
73
I2C 2Kbit
EEPROM
Slide 73
To the PC
parallel
port
The I2C 2002-1A I2C evaluation board can be
purchased from http://www.demoboard.com for $199.
To the I2C
Evaluation Board
I2C bus signals
Jumper JP2
I2C Voltage Selection (Bus
voltage)
Open = 3.3 V bus
Closed = 5.0 V bus
Demo boards include at demoboard.com include:
DesignCon 2003 TecForum I2C Bus Overview
I2C-Trace: I2C Bus Tracer Kit - I2C Monitor captures
and displays I2C bus messages on any PC
Slide 75
WIN-SMBUS: SMBUS Protocol S/W-H/W Kit Supports SMBus ICs and the SMBus v1.0 protocol
26
75
AN10216-01 I2C Manual
The I2CPORT v2 adapter card plugs into the parallel
port and provides the interface between the Personal
Computer and the I2C bus operating up to 150 kHz.
27
AN10216-01 I2C Manual
Device Æ I/O Expanders Æ PCA9501
Evaluation Board I2C 2002-1A Overview
GPIO register value
I2C 2002-1A Evaluation Board
Main I2C Bus
SCL/SDA
1
GPIO value
PCA9550
PCA9551
PCA9554
PCA9543
PCA9555
PCA9561
PCA9501
PCF8582
LM75A
LM75A
PCA9515
USB A
SCL1/SDA1
GPIO
address
EEPROM
address
P82B96
RJ11
SCL2/SDA2
3
9V
REGULATORS
3.3 V
3
5.0 V
2
Byte 8BH
or 13910
EEPROM
Read /
Write
Options
Set the all
EEPROM to
the same
value
• 12 I2C devices on the evaluation board
• 2 evaluation boards can be daisy chained without any address conflict
• Boards cascadable through I2C connectors, RJ11 phone cable or USB cable
• On board regulators
DesignCon 2003 TecForum I2C Bus Overview
Auto Write
Feature
Write Time
USB B
SCL0/SDA0
GPIO
programming
Selected byte
information
3
4
GPIO Read / Write Options
1
EEPROM
programming
DesignCon 2003 TecForum I2C Bus Overview
76
78
Slide 76
Slide 78
There are many new I2C devices on the evaluation
board including GPIO, LED Blinkers, Switches, DIP
Switches and Bus Buffers.
Slide 78 shows the 8 bit GPIO and 2 kbit EEPROM
selection for the PCA9501.
Device Æ Multiplexers/Switches Æ PCA9543
Win-I2CNT Screen Examples
Starting the Software
Device address
Clicking on the Win- I2CNT icon will start the software and will
give the following window
Control Register
Value
Read / Write
Operation
Working Window
Selection
Open the
Universal
modes
screen
Channel
Selection
Open the device
specific screen
2 modes for the clock.
Slow is adequate for
slow ports and to solve
some potential
compatibility issue
Interrupt
Status
I2C Indicates the
clock (SCL)
frequency
Indicates that I2C communications can
start
If problem, message “WIN-I2C hardware
not detected” displayed
Æ Action: check Adapter Card
Auto Write
Feature
DesignCon 2003 TecForum I2C Bus Overview
Help Hints
DesignCon 2003 TecForum I2C Bus Overview
79
Parallel Port
Slide 79
77
Slide 79 shows the selection possibilities for the
PCA9543/45/46/48 switches.
Slide 77
Slide 77 shows the start screen from which all the other
screens are selected.
Device Æ LED Drivers/Blinkers Æ PCA9551
LED drivers
states
Register values
Device
address
Auto Write
Feature
Read / Write
Operation
Frequencies
and duty cycles
programming
DesignCon 2003 TecForum I2C Bus Overview
Slide 80
28
80
AN10216-01 I2C Manual
Device Æ Non-Volatile Registers Æ PCA9561
Slide 80 shows the selections for the PCA9551 8 bit
LED Blinker. The PCA9551 has two PWMs and
controls for each bit (ON, OFF, BLINK1 and
BLINK2).
Device
Address
EEPROMs
Read / Write
Operation
Device Æ I/O Expanders Æ PCA9554
Auto Write
Feature
Output
Register
MUX_IN
Read
Operation
Read / Write
Operation (all
registers)
Data
(EEPROM,
MUX_IN)
Multiplexing
Device
address
Configuratio
n Register
Input
Register
Note: MUX_IN, MUX_SELECT and WP pins are not controlled by the Software
DesignCon 2003 TecForum I2C Bus Overview
83
Polarity
Register
Register
Programming
Slide 83
Read / Write
Operation
(specific
register)
DesignCon 2003 TecForum I2C Bus Overview
Slide 83 shows the PCA9561 6 bit DIP Switch along
with the 4 bit PCA8550 and 6 bit PCA9559/60.
81
Device Æ Thermal Management Æ LM75A
Slide 81
Polarity
Registers
Input
Registers
Temperature
monitoring
Device
address
Read / Write
Operation
(specific register)
Device
modes
Device Æ I/O Expanders Æ PCA9555
Auto Write
Feature
Read / Write
Operation (all
registers)
Auto Write
Feature
Slide 81 shows the 8 bit true output GPIO. Controls
allow to:
- Program the bits a inputs or outputs
- Program the output state of output bits
- Read the logic state in each input or output pin
- Invert or not the bits that have been read
Read / Write Operation
(all registers)
Temperature
Monitoring
Programming
frequency
DesignCon 2003 TecForum I2C Bus Overview
Device
Address
Start
Monitoring
84
Slide 84
Register
Programming
Output
Registers
Slide 84 allows control of the LM75A and monitoring
of the temperature on the graph.
Configuration
Registers
Read / Write
Operation
(specific Register)
Device Æ EEPROM Æ 256 x 8 (2K)
DesignCon 2003 TecForum I2C Bus Overview
• Control window and operating scheme same as PCA9501’s 2KBit EEPROM
82
PCA9515
Slide 82
• Bus repeater - No software to control it
• Buffered I2C connector available
Slide 82 shows the 16 bit true output GPIO.
• Enable Control pin accessible
P82B96
• Bus buffer - No software to control it
• I2C can come from the Port Adapter + USB Adapter through the USB
cable
• I2C can be sent through RJ11 and USB cables to others boards
• 5.0 V and 9.0 V power supplies
DesignCon 2003 TecForum I2C Bus Overview
Slide 85
29
85
AN10216-01 I2C Manual
Slide 85 discusses the devices on the I2C 2002-1A
evaluation board that is not controlled via the I2C bus.
They just provide the possibility to expand/extend the
internal 3.3V I2C bus to external devices.
How to program the Universal Screen?
• Length of the messages is variable: 20 instructions max
• 5 different messages can be programmed
PCA9515 allows connection using short wiring to
another 400 pF bus having 3.3-5 V standard I2C chips.
• First START and STOP instructions can not be removed
• I2C Re-Start Command Æ “S” key
• I2C Write Command Æ “W” key
P82B96 allows options to demonstrate:
1. Linking to a second evaluation board using a
USB cable to provide the power and I2C data
link to it.
2. Linking two evaluation boards using a very
long telephony cable, say 10 m/33 ft or even
more.
3. Linking the evaluation board via a USB cable
to the I2CPORT v2 adapter card. It allows a
more convenient separation up to 5 m. Just
include the USB adapter card.
4. Expanding to another fully standard I2C bus
operating at any desired voltage from 2 V to
15 V.
• I2C Read Command Æ “R” key
• Add an Instruction Æ “Insert” key
• Remove an Instruction Æ “Delete” key
• Data: 0 to 9 + A to F keys
DesignCon 2003 TecForum I2C Bus Overview
87
Slide 87
Slide 87 shows how easy it is to program the universal
programming screen.
Some others interesting Features
See AN10146-01 for full details.
• I2C clock frequency can be modified (Options Menu).
• Acknowledge can be ignored for stand alone experiment
(Options Menu).
Universal Receiver / Transmitter Screen
• Universal Transmitter/Receiver program can be saved in a file.
• Device specific screens are different depending on the selected device.
All the options are usually covered in those screens.
Good tool to learn how the devices work and test all the features.
Commands
Programming
• Possibility to build some small applications by connecting the devices
together through the headers.
I2C
sequencing
parameters
DesignCon 2003 TecForum I2C Bus Overview
88
Slide 88
Sequencer
Send
Sequence
selected
programming
message
DesignCon 2003 TecForum I2C Bus Overview
There are many interesting features in the Win-I2CNT
system that can help experiment with the new I2C
devices.
Programmable delay
between the messages
86
Slide 86
Slide 86 shows the universal screen where I2C
command sequence can be used to program any device.
30
AN10216-01 I2C Manual
http://300pinmsa.org/document/MSA_10G_40G_TRX_
I2C_Public_Document_02_19APR02.pdf
So the idea is to look to any general systems that use
dynamic address allocation (even including ones that do
not use I2C hardware) to find the software design ideas
for building these systems.
How to Order the I2C 2002-1A Evaluation Kit
How To Obtain the New Evaluation Kit
• The I2C 2002-1A Evaluation Board Kit consists of the:
– I2C 2002-1A Evaluation Board
– I2CPort v2 Adapter Card for the PC parallel port
– 4-wire connector cable
– USB Adapter Card (no USB cable included)
– 9 V power supply
– CD-ROM with operating instructions and Win-I2CNT software on
that provides easy to use PC graphical interface specific to the I2C
devices on the evaluation board but also with general purpose
mode for all other I2C devices.
I2C Bus Vs SMBus - Electrical Differences
Purchase the I2C 2002-1A Evaluation Board Kit
at www.demoboard.com
DesignCon 2003 TecForum I2C Bus Overview
89
Slide 89
Comparison of I2C with SMBus
Low Power version of the SMBus Specification only
The SMBus specification can be found on SMBus web site at www.SMBus.org
DesignCon 2003 TecForum I2C Bus Overview
Some words on SMBus
93
Slide 93
• Protocol derived from the I2C bus
• Original purpose: define the communication link between:
SMBus is used today as a system management bus in
most PCs. Developed by Intel and others in 1995, it
modified some I2C electrical and software
characteristics for better compatibility with the quickly
decreasing power supply budget of portable equipment.
– an intelligent battery
– a charger
– a microcontroller
• Most recent specification: Version 2.0
– Include a low power version and a “normal” power version
– can be found at: www.SMBus.org
• Some minor differences between I2C and SMBus:
SMBus also has a "High Power" version 2.0 that
includes a "4 mA sink current" version that strictly
cannot be driven by I2C chips.
– Electrical
– Timing
– Operating modes
DesignCon 2003 TecForum I2C Bus Overview
92
I2C Bus Vs SMBus - Timing and operating
modes Differences
Slide 92
The SMBus uses I2C hardware, and I2C hardware
addressing, but adds second-level software for building
special systems. In particular its specifications include
"Address Resolution Protocol" that can make dynamic
address allocations.
• Timing:
– Minimum clock frequency = 10 kHz
– Maximum clock frequency = 100 kHz
– Clock timeout = 35 ms
• Operating modes
"Dynamic reconfiguration: The hardware and software
allow bus devices to be "hot-plugged" and used
immediately, without restarting the system. The devices
are recognized automatically and assigned unique
addresses. This advantage results in a plug-and-play
user interface." In both those protocols there is a very
useful distinction made between a System Host and all
the other devices in the system that can have the names,
and functions, of masters or slaves.
– slaves must acknowledge their address all the time
(mechanism to detect a removable device’s presence)
DesignCon 2003 TecForum I2C Bus Overview
94
Slide 94
I2C/SMBus compliancy
SMBus and I2C protocols are basically the same: A
SMBus master will be able to control I2C devices and
vice-versa at the protocol level. The SMBus clock is
defined from 10 kHz to 100 kHz while I2C can be a DC
I2C is also used as the hardware bus with some form of
dynamic address assignment in the Optical network
module specifications you can find at this website:
31
AN10216-01 I2C Manual
bus (0 to 100 kHz, 0 to 400 kHz, 0 to 3.4 MHz). This
means that an I2C bus running at a frequency lower than
10 kHz will not be SMBus compliant since the
specification does not allow it.
Philips SMBus “high power” devices are also
electrically compatible with I2C specifications but
SMBus devices from others may not always be
compatible with I2C. Philips I2C devices are electrically
compatible with low power SMBus specifications but
will not normally conform to all its software features
like time-out.
Logic levels are slightly different also: TTL for SMBus:
low = 0.8V and high = 2.1V, 30%/70% VDD CMOS
level for I2C. This is not a big deal if VDD > 3.0 V. If the
I2C device is below 3.0 V then there is a problem since
the logic hi/lo levels may not be recognized.
Example for a typical I2C slave device, the PCA9552. It
will be SMBus compliant if:
- 10 kHz < Fclock < 100 kHz
- It the device works in a 3.3V or higher
environment
Timeout feature: SMBus has a timeout feature, resetting
the devices if a communication takes too long (thus
explaining the min clock frequency at 10 kHz). I2C can
be a "DC" bus meaning that a slave device stretches the
master clock when performing some routine while the
master is accessing it. This will notify to the master:
"I'm busy right now but I do not want to loose the
communication with you, so hold on a little bit and I
will let you continue when I'm done" ... and a "little bit"
can be an eternity, (at least lower than 10 kHz).
Note: the PCA9552 will not be able to reset itself if the
bus communication time is higher than the timeout
value. That is pretty much the case for all Philips
devices. Often the time-out feature can be added for a
few cents in discrete hardware. See Slide 57.
SMBus protocol just assumes that if something takes
too long, then it means that there is a problem in the bus
and that everybody must reset in order to clear this
mode. Slave devices are not then allowed to hold the
clock low too long.
Intelligent Platform Management Interface
(IPMI)
Intel initiative in conjunction with hp, NEC and Dell
and consists of three specifications:
• IPMI for software extensions
• Intelligent Platform Management Bus (IPMB) for
intra-chassis (in side the box) extensions
• Inter Chassis Management Bus (ICMB) for interchassis (outside of the box) extensions
Differences SMBus 1.0 and SMBus 2.0
Here is the statement from the SMBus 2.0 document:
This specification defines two classes of electrical
characteristics, low power and high power. The first
class, originally defined in the SMBus 1.0 and 1.1
specifications, was designed primarily with Smart
Batteries in mind, but could be used with other lowpower devices.
Needed since as the complexity of systems increase,
MTBF decreases. IPMI defines a standardized,
abstracted, message-based interface to intelligent
platform
management
hardware
are
defines
standardized records for describing platform
management devices and their characteristics. IPMI
provides a self monitoring capability increasing
reliability of the systems
This 2.0 version of the specification introduces an
alternative higher power set of electrical characteristics.
This class is appropriate for use when higher drive
capability is required, for example with SMBus devices
on PCI add-in cards and for connecting such cards
across the PCI connector between each other and to
SMBus devices on the system board.
IPMI
Provides a self monitoring capability increasing
reliability of the systems
Monitor server physical health characteristics:
• Temperatures
• Voltages
• Fans
• Chassis intrusion
Devices may be powered by the bus VDD or by another
power source, VBus, (as with, for example, Smart
Batteries) and will inter-operate as long as they adhere
to the SMBus electrical specifications for their class.
Philips devices have a higher power set of electrical
characteristics than SMBus1.0.
General system management:
• Automatic alerting
• Automatic system shutdown and re-start
• Remote re-start
• Power control
Main parameter is the current sink capability with Vol
= 0.4V.
- SMBus low power = 350 uA
- SMBus high power = 4 mA
- I2C = 3 mA
32
AN10216-01 I2C Manual
More information:
www.intel.com/design/servers/ipmi/ipmi.htm
Overall IPMI Architecture
ICMB
Standardized bus and protocol for extending
management control, monitoring, and event delivery
within the chassis:
• I2C based
• Multi-master
• Simple Request/Response Protocol
• Uses IPMI Command sets
• Supports non-IPMI devices
• Physically I2C but write only (master capable
devices), hot swap not required.
• Enables the Baseboard Management Controller
(BMC) to accept IPMI request messages from
other management controllers in the system.
• Allows non-intelligent devices as well as
management controllers on the bus.
• BMC serves as a controller to give system software
access to IPMB
IPMB
BMC
DesignCon 2003 TecForum I2C Bus Overview
100
Slide 100
Where IPMI is being used
Intel Server Management
Servers today run mission-critical applications. There is
literally no time for downtime. That is why Intel created
Intel® Server Management – a set of hardware and
software technologies built right into most Intel® sever
boards that monitors and diagnoses server health. Intel
Server Management helps give you and your customers
more server uptime, increased peace of mind, lower
support costs, and new revenue opportunities.
Defines a standardized interface to intelligent platform
management
Hardware
• Prediction and early monitoring of hardware
failures
• Diagnosis of hardware problems
• Automatic recovery and restoration measures after
failure
• Permanent availability management
• Facilitate management and recovery
• Autonomous Management Functions: Monitoring,
Event Logging, Platform Inventory, Remote
Recovery
More information:
http://program.intel.com/shared/products/servers/boards
/server_management
PICMG
PICMG (PCI Industrial Computer Manufacturers
Group) is a consortium of over 600 companies who
collaboratively develop open specifications for high
performance telecommunications and industrial
computing applications. PICMG specifications include
CompactPCI® for Eurocard, rack mount applications
and PCI/ISA for passive backplane, standard format
cards. Recently, PICMG announced it was beginning
development of a new series of specifications, called
AdvancedTCA™,
for
next-generation
telecommunications equipment, with a new form factor
and based on switched fabric architectures.
Implemented
using
Autonomous
Management
Hardware:
Designed for Microcontrollers based implementations
Hardware implementation is isolated from software
implementation
New sensors and events can then be added without any
software changes
More information can be found at:
http://www.picmg.org
33
AN10216-01 I2C Manual
Use of IPMI within PICMG
Known as
Specification
Based on
Comments
cPCI
PICMG 2.0
NA
No IPMB
cPCI
PICMG 2.9
IPMI 1.0
Single hot swap IPMB optional
AdvancedTCA
PICMG 3.x
IPMI 1.5
Dual redundant hot swap IPMB mandatory
Slide 106 shows one of the two redundant buses that
would interface through the PCA9511 or
PCA9512/13/14.
VME
• PICMG 2.0: CompactPCI Core
• Motorola, Mostek and Signetics
cooperated to define the standard
• PICMG 2.9: System Management
• PICMG 3.0: AdvancedTCA Core
• Mechanical standard based on the
Eurocard format.
• 3.1 Ethernet Star (1000BX and XAUI) – FC-PH links mixed with 1000BX
• 3.2 InfiniBand® Star & Mesh
• Large body of mechanical
hardware readily available
• 3.3 StarFabric
• Pin and socket connector scheme
is more resilient to mechanical wear
than older printed circuit board
edge connectors.
• 3.4 PCI Express
DesignCon 2003 TecForum I2C Bus Overview
104
• Hundreds of component
manufacturers support applications
such as industrial controls, military,
telecommunications, office automation
and instrumentation systems.
Slide 104
IPMI with additional extension is used as the basis for
PICMG 2.9 and PICMG 3.x.
DesignCon 2003 TecForum I2C Bus Overview
VMEbus
VMEbus is a computer architecture. The term 'VME'
stands for VERSAmodule Eurocard and was first
coined in 1980 by the group of manufacturers who
defined it. This group was composed of people from
Motorola, Mostek and Signetics corporations who were
cooperating to define the standard. The term 'bus' is a
generic term describing a computer data path, hence the
name VMEbus. Actually, the origin of the term 'VME'
has never been formally defined. Other widely used
definitions are VERSAbus-E, VERSAmodule Europe
and VERSAmodule European. However, the term
'Eurocard' tends to fit better, as VMEbus was originally
a combination of the VERSAbus electrical standard,
and the Eurocard mechanical form factor.
PCA9511
• Dual, redundant -48VDC power distribution to each
card w. high current, bladed power connector
• High frequency differential data connectors
• Robust keying block
• Two alignment pins
• Robust, redundant system management
• 8U x 280mm card size
• 1.2” (6HP) pitch
• Flexible rear I/O connector area
DesignCon 2003 TecForum I2C Bus Overview
105
Slide 105
Slide 105 shows how IPMI is used within an
AdvancedTCA card.
VERSAbus was first defined by Motorola Corporation
in 1979 for its 68000 microprocessor. Initially, it
competed with other buses such as Multibus™, STD
Bus, S-100 and Q-bus. However, it is rarely used
anymore. The microcomputer bus industry began with
the advent of the microprocessor, and in 1980 many
buses were showing their age. Most worked well with
only one or two types of microprocessors, had a small
addressing range and were rather slow. The VMEbus
architects were charged with defining a new bus that
would be microprocessor independent, easily upgraded
from 16 to 32-bit data paths, implement a reliable
mechanical standard and allow independent vendors to
build compatible products. No proprietary rights were
assigned to the new bus, which helped stimulate third
party product development. Anyone can make VMEbus
products without any royalty fees or licenses. Since
much work was already done on VERSAbus it was
used as a framework for the new standard.
Managed ATCA Shelf: Example 1
PCA9511 PCA9511 PCA9511 PCA9511
PCA9511 PCA9511
PCA9511 PCA9511 PCA9511 PCA9511 PCA9511 PCA9511 PCA9511 PCA9511 PCA9511 PCA9511 PCA9511 PCA9511 PCA9511 PCA9511 PCA9511 PCA9511
DesignCon 2003 TecForum I2C Bus Overview
107
Slide 107
Managed ATCA Board Example
PCA9511
www.vita.com
106
Slide 106
34
AN10216-01 I2C Manual
I2C Device Overview
In addition, a mechanical standard based on the
Eurocard format was chosen. Eurocard is a term that
loosely describes a family of products based around the
DIN 41612 and IEC 603-2 connector standards, the
IEEE 1101 PC board standards and the DIN 41494 and
IEC 297-3 rack standards. When VMEbus was first
developed, the Eurocard format had been well
established in Europe for several years. A large body of
mechanical hardware such as card cages, connectors
and sub-racks were readily available. The pin and
socket connector scheme is more resilient to
mechanical wear than older printed circuit board edge
connectors.
I2C Device Categories
The marriage of the VERSAbus electrical specification
and the Eurocard format resulted in VMEbus Revision
A. It was released in 1981. The VMEbus specification
has since been refined through revisions B, C, C.1, IEC
821, IEEE 1014-1987 and ANSI/VITA 1-1994. The
ANSI, VITA, IEC and IEEE standards are important
because they make VMEbus a publicly defined
specification. Since no proprietary rights are assigned to
it, vendors and users need not worry that their products
will become obsolete at the whim of any single
manufacturer. Since its introduction, VMEbus has
generated thousands of products and attracted hundreds
of manufacturers of boards, mechanical hardware,
software and bus interface chips. It continues to grow
and support diverse applications such as industrial
controls,
military,
telecommunications,
office
automation and instrumentation systems.
• TV Reception
• General Purpose I/O
• Radio Reception
• LED display control
• Audio Processing
• Bus Extension/Control
• Infrared Control
• A/D and D/A Converters
• DTMF
• EEPROM/RAM
• LCD display control
• Hardware Monitors
• Clocks/timers
• Microcontroller
DesignCon 2003 TecForum I2C Bus Overview
110
Slide 110
I2C devices can be broken down into different
categories.
• TV reception: Provides TV tuning and reception
• Radio reception: Provides radio tuning and
reception
• Audio Processing
• Infra-Red control
• DTMF: Dual Tone Multiple Frequency
• LCD display control: Provides power to segments
of an LCD that are controlled via I2C bus
• LED display control: Provides power to segments
of an LED that are controlled via I2C bus
• Real time clocks and event counters: counting the
passage of time, chronometer, periodic alarms for
safety applications, system energy conservation,
time and date stamp for point of sales terminals or
bank machines.
• General Purpose Digital Input/Output (I/O):
monitoring of ‘YES’ or ‘NO’ information, such as
whether or not a switch is closed or a tank
overflows; or controlling a contact, turning on an
LED, turning off a relay, starting or stopping a
motor, or reading a digital number presented at the
port (via a DIP switch, for example).
• Bus Extension/Control: expends the I2C bus
beyond the 400 pF limit, allows different voltage
devices on the same I2C bus or allows devices with
the same I2C address to be selectively addressed on
the I2C bus.
• Analog/digital conversion: measurement of the size
of a physical quantity (temperature, pressure…),
proportional control; transformation of physical
analog values into numerical values for calculation.
• Digital/analog conversion: creation of particular
control voltages to control DC motors or LCD
contrast.
• RAM: Random Access Memory
Use of IPMI in VME Architecture
New VME draft standard indirectly calls for IPMI over
I2C for the system management protocol since there
was nothing to be gained by reinventing a different
form of system management for VME. The only change
from the PICMG 2.9 system management specification
is to redefine the backplane pins used for the I2C bus
and to redefine the capacitance that a VME board can
present on the I2C bus. The pin change was required
because the VME backplane connectors are different
from cPCI. The capacitance change was required
because cPCI can have a maximum of 8 slots and VME
can have a maximum of 21 slots. System Management
for VME Draft Standard VITA 38 – 200x Draft 0.5 9
May 02 draft at:
http://www.vita.com/vso/draftstd/vita38.d0.5.pdf
provides more information.
35
AN10216-01 I2C Manual
•
•
•
I2C devices are designed in the process that allows best
electrical and ESD performance and are manufactured
in Philips or third party fabs through out the world.
Philips has taken the initiative to offer the same process
in multiple internal fabs to provide redundancy and
continuation of supply in any market condition.
EEPROM: Electrically Erasable Programmable
Read Only Memory, retains digital information
even when powered down
Hardware Monitors: monitoring of the temperature
and voltage of systems
Microprocessors: Provides the brains behind the
I2C bus operation.
TV Reception
I2C Product Characteristics
TV Reception
• Package Offerings
Typically DIP, SO, SSOP, QSOP,
TSSOP or HVQFN packages
• Frequency Range
Typically 100 kHz operation
Newer devices operating up to 400 kHz
Graphic devices up to 3.4 MHz
• Operating Supply Voltage Range
2.5 to 5.5 V or 2.8 to 5.5 V
Newer devices at 2.3 to 5.5 V or 3.0 to 3.6 V with 5 V tolerance
• Operating temperature range
Typically -40 to +85 ºC
Some 0 to +70 ºC
• Hardware address pins
Typically three (AO, A1, A2) are provided to allow up to eight of the
identical device on the same I2C bus but sometimes due to pin
limitations there are fewer address pins
DesignCon 2003 TecForum
I2C
Bus Overview
The SAA56xx family of microcontrollers are
a derivative of the Philips industry-standard
80C51 microcontroller and are intended for
use as the central control mechanism in a
television receiver. They provide control
functions for the television system, OSD and
incorporate an integrated Data Capture and
display function for either Teletext or Closed
Caption.
Additional features over the SAA55xx family have been included, e.g. 100/120
Hz (2H/2V only) display timing modes, two page operation (50/60 Hz mode for
16:9, 4:3), higher frequency microcontroller, increased character storage, more
80C51 peripherals and a larger Display memory. For CC operation, only a
50/60 Hz display option is available.
Byte level I²C-bus up to 400 kHz dual port I/O
DesignCon 2003 TecForum I2C Bus Overview
111
112
Slide 111
Slide 112
The frequency range of most of the newer I2C devices
is up to 400 kHz and we are moving to 3.4 MHz for
future devices where typical uses would be in consumer
electronics where a DSP is the master and the designer
wants to rapidly send out the I2C information and then
move on to other processing needs.
The I2C bus is used as a means to easily move control
or status information on and off the devices. The
SA56xx is given as an example of this type of device.
Radio Reception
Radio Reception
The operating range of most of the newer CMOS
devices is 2.3 to 5 V to allow operation at the 2.5, 3.3
and 5V nodes. Some processes restrict the voltage
range to the 3.3 V node. Most customers have moved
from 5 V and are now at 3.3 V but several are moving
rapidly to 2.5 V and even 1.8 V in the near future. We
are working on next generation general purpose devices
to support 1.8 V operation and currently have some
LCD display drivers that operate down to 1 V.
The TEA6845H is a
single IC with car
radio tuner for AM
and FM intended
for microcontroller
tuning with the I²Cbus. It provides the
following functions:
• AM double conversion receiver for LW, MW and SW (31 m, 41 m and 49 m
bands) with IF1 = 10.7 MHz and IF2 = 450 kHz
The operating temperature range is typically specified
at the industrial temperature range but again depending
on process or application, the range may be specified
higher or lower. The automotive, military and aviation
industries have expressed more interest in I2C devices
due to the low cost and simplicity of operation so future
devices temperature ranges may be expanded to meet
their needs.
• FM single conversion receiver with integrated image rejection for IF = 10.7 MHz
capable of selecting US FM, US weather, Europe FM, East Europe FM and Japan
FM bands.
DesignCon 2003 TecForum I2C Bus Overview
113
Slide 113
Again, the I2C bus is used to control frequency
selection or control the audio sound control and
interface with the microcontroller. Special software
programs, applied by connecting to the I2C bus during
factory testing, automatically perform the alignment of
the RF sections of the receiver, eliminating the need for
manual or mechanical adjustments. The alignment
information will be stored in some non-volatile memory
I2C devices were typically offered in either DIP or SO
and limited their use in equipment where space is at a
premium. Newer I2C devices are typically offered in
SO, TSSOP or near chip scale HVQFN packages.
36
AN10216-01 I2C Manual
chip voltage reference the PCD3311C and PCD3312C
provide constant output amplitudes that are independent
of the operating supply voltage and ambient
temperature. An on-chip filtering system assures a very
low total harmonic distortion in accordance with CEPT
recommendations. In addition to the standard DTMF
frequencies the devices can also provide:
• Twelve standard frequencies used in simplex
modem applications for data rates from 300 to
1200 bits per second
• Two octaves of musical scales in steps of
semitones.
chip and re-sent to the receiver chip, where it is stored
in R.A.M., each time power is applied to the receiver.
Audio Processing
Audio Processing
The SAA7740H is a functionspecific digital signal processor.
The device is capable of
performing processing for
listening-environments such as
equalization, hall-effects,
reverberation, surround-sound
and digital volume/balance
control. The SAA7740H can
also be reconfigured (in a dual
and quad filter mode) so that it
can be used as a digital filter
with programmable
characteristics.
LCD Display Driver
The SAA7740H realizes most functions directly in hardware. The flexibility exists in
the possibility to download function parameters, correction coefficients and various
configurations from a host microcontroller. The parameters can be passed in real
time and all functions can be switched on simultaneously. The SAA7740H accepts
2 digital stereo signals in the I2S-bus format at audio sampling frequency (fast )
and provides 2 digital stereo outputs.
DesignCon 2003 TecForum I2C Bus Overview
I2C LCD Display Driver
LCD Display Control
Display size:
2 line by 12 characters +
120 icons
114
DDRAM
Row driver
Slide 114
The I2C bus is used to control the audio and sound
balance.
Sequencer
CGRAM
Control
logic
SDA
SCL
CGROM
Bias voltage Voltage
generator
multiplier
Supply
Column driver
The LCD Display driver is a complex device and is an
example of how "complete" a system an I2C chip can be –
it generates the LCD voltages, adjusts the contrast,
temperature compensates, stores the messages, has
CGROM and RAM etc etc.
Dual Tone Multi-Frequency (DTMF)
DTMF/Modem/Musical Tone Generators
DesignCon 2003 TecForum I2C Bus Overview
116
Slide 116
The LCD display driver is a complex LCD driver and is
an example of how "complete" a system an I2C chip can
be - generates the LCD voltages, adjusts the contrast,
temperature compensates, stores the messages, has
CGROM and RAM etc.
• Modem and musical tone generation
• Telephone tone dialing
• DTMF > Dual Tone Multiple Frequency
• Low baud rate modem
DesignCon 2003 TecForum I2C Bus Overview
I2C LCD Segment Driver
115
Display sizes
1 x 24 … 2 x 40…
single chip: 4 x 40 ... 16 x 24
LCD Segment Control
Slide 115
Control logic
SCL
Supply
RAM
Bias voltage
generator
Sequencer
The PCD3311C and PCD3312C are single-chip silicon
gate CMOS integrated circuits. They are intended
principally for use in telephone sets to provide the dualtone multi-frequency (DTMF) combinations required
for tone dialing systems. The various audio output
frequencies are generated from an on-chip 3.58 MHz
quartz crystal-controlled oscillator. A separate crystal is
used, and a separate microcontroller is required to
control the devices.
Backplane drivers
SDA
Segment drivers
The LCD Segment driver is a less complex LCD driver
(e.g., just a segment driver).
DesignCon 2003 TecForum I2C Bus Overview
117
Slide 117
Both the devices can interface to I2C bus compatible
microcontrollers for serial input. The PCD3311C can
also interface directly to all standard microcontrollers,
accepting a binary coded parallel input. With their on-
The LCD segment driver is a less complex LCD driver
(e.g., just a segment driver). Philips focus is for large
37
AN10216-01 I2C Manual
recently developed and is technically the most
advanced. The RTCs have one interrupt output and do
not track the exact year. This must be done in software
by the customer. They do use a 4-year calendar base
and can count 255 years. PCF8583 has the added
advantage of 240 bytes of RAM integrated with the
RTC. This could be important if such small RAM is
required then we replace two chips with one.
volume consumer display apps, which is right now
B&W and color STN LCD displays and in near future it
will be TFT and OLED (organic LED displays). The
OLED drivers will most probably not be useable with
conventional LEDs.
VGA is beyond our current roadmap that stretches only
up to about 1/4 VGA. This is simply because of the
requirements that we see in the mobile telecomm
market, our main focus. We find already that I2C does
not give us enough transmission rate for display data so
serial bus is mainly intended for control and text
overlay signals in such displays.
General Purpose I/O Expanders
I2C General Purpose I/O Expanders
General Purpose I/O
Light Sensor
SDA
SCL
I2C-bus
interface
Sub
address
decoder
I2C Light Sensor
alternative analog
input configurations
≠
• Transfers keyboard, ACPI Power switch, keypad, switch or other inputs
to microcontroller via I2C bus
• Expand microcontroller via I2C bus where I/O can be located near the
source or on various cards
• Use outputs to drive LEDs, sensors, fans, enable and other input pins,
relays and timers
• Quasi outputs can be used as Input or Output without the use of a
configuration register.
The TSL2550 sensor converts the intensity of ambient light into digital signals
that, in turn, can be used to control the backlighting of display screens found in
portable equipment, such as laptops, cell phones, PDAs, camcorders, and GPS
systems. The device can also be used to monitor and control commercial and
residential lighting conditions.
By allowing display brightness to be adjusted to ambient conditions, the sensor
is expected to bring about a significant reduction in the power dissipation of
portables.
DesignCon 2003 TecForum I2C Bus Overview
The TSL2550 all-silicon sensor combines two photodetectors, with one of the
detectors sensitive to both visible and infrared light and the other sensitive only
to IR light. The photodetectors’s output is converted to a digital format, in which
form the information can be used to approximate the response of the human
eye to ambient light conditions sans the IR element, which the eye cannot
perceive.
DesignCon 2003 TecForum I2C Bus Overview
Interrupt
Input/ output stages
POR
Latches
Supply
120
Slide 120
Let’s talk about some of the newer devices, such as
these new general-purpose input and output (GPIO)
expansion for the I2C/SMBus.
118
Slide 118
Slide 118 shows a new innovation in light detectors that
uses the I2C bus to transfer information to and from the
sensor.
Quasi Output I2C I/O Expanders - Registers
• To program the outputs
S
Real Time Clock/Calendar
32kHz
Counters:
s, min, h, day,
month, year
Alarm-, TimerRegisters
(240 Byte RAM 8583)
Interrupt
Oscillator /
prescaler
I2C-bus
interface
S
SDA
SCL
Sub
address
decoder
DesignCon 2003 TecForum I2C Bus Overview
A
OUTPUT
DATA
A
P
R
A
INPUT
DATA
A
P
Multiple reads are
possible during the
same communication
– At power-up, all the I/O’s are HIGH; Only a current source to VDD is
active
– An additional strong pull-up resistors allows fast rising edges
– I/O’s should be HIGH before using them as Inputs
• periodic alarms for
safety applications
DesignCon 2003 TecForum I2C Bus Overview
• system energy
conservation
• time and date stamp
for point of sales
terminals or bank
machines
Address
Multiple writes are
possible during the
same communication
• Important to know
Real time clocks and
event counters count
the passage of time and
act as a chronometer
They are used in
applications such as:
POR
W
• To read input values
I2C Real Time Clock/Calendar
Real-Time Clock / Calendar
Address
121
Slide 121
The PCF8574 and PCA8575 are well known general
purpose I/O expanders. The PCA9500 is a combination
of the PCF8574 with a 2K EEPROM. The interrupt pin
is replaced by the EEPROM write protect (WP). The
EEPROM has a different fixed I2C address then the
GPIO. The PCA9501 is a combination of the PCF8574
with a 2K EEPROM. The device is offered in a 20-pin
TSSOP package and the four extra pins allow the
119
Slide 119
Philips offers four RTCs, these are PCF8593, PCF8583,
PCF8573 and PCF8563. The PCF8563 is the most
38
AN10216-01 I2C Manual
interrupt output to be included in addition to the WP.
The extra three pins are then used to offer a total of six
address pins allowing up to 64 of these devices to share
the same I2C bus. The PTN devices are design for
telecom maintenance and control applications.
True Output I2C I/O Expanders - Example
The PCA9558 is a combination of the PCA9557 with a
2K EEPROM and 5-bit DIP Switch.
True Output
I2C
I/O Expanders - Registers
• To configure the device
S
Address
W
A
03H
A
CONFIG
DATA
A
S
Address
W
A
02H
A
POLARITY
DATA
A
P
Address
W
A
01H
Address
W
A
00H
Config
Reg#
Output
Reg#
1
0
1
X
1
1
0
0
1
1
0
0
0
0
0
0
1
0
1
1
0
1
1
X
1
1
1
1
X
0
0
0
1
X
0
1
0
0
1
Read
Read/
Write
Read/
Write
Read/
Write
1
I/O’s
DesignCon 2003 TecForum I2C Bus Overview
OUTPUT
DATA
A
A
P
R
A
Multiple writes are
possible during the
same communication
Slide 124 shows an example
PCA9554/54A/57 is programmable.
• To read input values
S
Polarity
Reg#
124
Slide 124
• To program the outputs
S
No need to access
Configuration and
Polarity registers
once programmed
Input
Reg#
A
S
Address
INPUT
DATA
A
how
the
P
Multiple reads are possible
during the same communication
DesignCon 2003 TecForum I2C Bus Overview
of
Signal monitoring and/or Control
123
• Advantages of I2C
Slide 123
– Easy to implement (Hardware and Software)
– Extend microcontroller: I/O’s can be located near the source or on
These newer device’s true outputs provide active source
and sink current sources and does not rely upon a pull
up resistor to provide the source current. The four sets
of registers within the true outputs devices are
programmable and provide for: Configuration (Input or
Output) control, Input (value), Output (value) or
Polarity (active high or low).
various cards
– Save GPIO’s in the microcontroller
– Only 2 wires needed, independently of the numbers of signals
– Signal(s) can be far from the masters
– Fast enough to control keyboards
– Simplify the PCB layout
– Devices exist in the market and are massively used
DesignCon 2003 TecForum I2C Bus Overview
The PCA9554/54A/55 devices have an interrupt output
and the 8 or 16 I/O pins can be configured for interrupt
inputs. These newly released devices have the same I2C
address and footprint as the PCF8574/74A/75 but
require some software modifications due to the
different I/O registers. The PCA9554 and PCA9555
have the same I2C address while the PCA9554A has a
slightly different fixed address allowing 16 devices
(eight 54A and eight 54/55 in any combination) to be
on the same I2C/SMBus. The PCA9556/57 feature a
Hardware Reset pin instead of the interrupt output that
allows the device to be reset remotely should the I2C
bus become hung up. The PCA9557 is an improved
version of the PCA9556 that has the electrical
characteristics of the PCA9554/54A. Information on
GPIO selection is contained within application note
AN469.
125
Slide 125
Signal Monitoring and/or Control first approach is to
use GPIO’s of the master(s) controlling the application.
In some applications, use of these GPIO’s is not the
best approach.
Reasons can be the following:
• Number of signals to monitor/control is too
important and requires a big amount of the
master’s GPIO’s.
• Signals can be in a remote location implying a
more complex PCB layout, with a lot of long traces
(making the design more sensitive to noise)
• Upgrade (more signals to monitor/control) requires
a total re-layout of the PCB and is limited to the
number of GPIO’s still available in the master.
39
AN10216-01 I2C Manual
tied up by sending repeated transmissions to blink
LEDs as is currently done when a GPIO is used. The
PCA9530/31/32/33 and the PCA9550/51/52/53 provide
the same amount of electrical sink capability as the
PCA9554/55/57 but have a built in oscillator and two
I2C programmable blink rates.
Signal monitoring and/or Control
• Proposed devices
# o f O u tp u ts
In te rru p t a n d
POR
P O R a n d 2K
EEP RO M
In te rru p t, P O R
a n d 2K EEP RO M
Q u a si O u tp u t (20-25 m a sin k a n d 100 u A so u rce )
8
P CF 8574/74A
P CA9500/58
P CA9501
16
P CF 8575/75C
-
# of Outputs
Reset and POR
Interrupt and POR
Two user definable blink rates and duty cycles
programmed via the I2C/SMBus. These are
programmed during the initial set up and can range
between 160 Hz and every 1.6 seconds for the LED
Dimmers and between 40 Hz and every 6.4 seconds for
the LED Blinkers. Thereafter only a single transmission
is required to turn individual LEDs: on, off or blink at
one of the two programmable blink rates. The duty
cycle can be used to ‘dim’ the LEDs using the LED
Dimmers by setting the blink rate to 160 Hz (faster than
the eye can see the blinking) and then changing the
average current through the LED by changing the duty
cycle.
True Output (20-25 ma sink and 10 mA source)
8
PCA9556/57
PCA9534/54/54A
16
PCA9535/55
• Advantages
– Number of I/O scalable
– Programmable I2C address allowing more than one device in the bus
– Interrupt output to monitor changes in the inputs
– Software controlling the device(s) easy to implement
DesignCon 2003 TecForum I2C Bus Overview
126
Slide 126
The I2C GPIO device approach provides an elegant
solution with minimum hardware and software changes:
• The device(s) can be plugged to an existing I2C bus
in the application
• Minor software change is required to control the
new device(s)
• Easily upgradeable (by adding more I2C GPIO
devices)
• Remote signals can be easily controlled (requires
only a longer I2C bus trace - 2 wires only)
• Changes in the monitored input signals can be
propagated to the master through a single Interrupt
line. The master can be easily interrogate the I2C
GPIO to determine which input(s) generated the
Interrupt
The internal oscillator is regulated to +/- 10% accuracy
and no external components are required. The +/- 10%
tolerance was recommended by human factor
engineers. These devices allow you to program two
specific blink rates and then command a LED to blink
at one of these rates without sending any further I2C
commands. If you use normal GPIOs to blink LEDs,
you must send an ON command followed by an OFF
command followed by an ON command for the
duration of the blink. This is OK if you do not have
many LEDs to blink or much traffic on the I2C bus, or
have microcontroller overhead to burn, but if you do
this for many LEDs you will tie up the I2C bus and your
micro controller. Hence the need for dedicated LED
blinkers as a stand alone part option. Unused pins can
be used as normal GP input or output, but since they are
open-drain, a pull up resistor will be needed for logic
high outputs.
See Application Note AN469 for more information on
GPIOs.
LED Dimmers and Blinkers
I2C LED Dimmers and Blinkers
Reset
POR
SCL
Sub address
decoder
≠
Input/ output stages
I2C-bus
interface
Oscillator
SDA
A Hardware Reset pin is included, allowing the LED
blinker to be reset independently from the rest of the
I2C/SMBus or higher level system. Each open drain
output can sink 25 mA of current with total package
sinking capacity limited to 100 mA for the 2, 4 and 8
bit devices and 200 mA for the 16 bit device (100 mA
for each byte). Typical LEDs take 10-25 mA of current
when in operation.
alternative analog input
configurations
Supply
• I2C/SMBus is not tied up by sending repeated transmissions to turn LEDs
on and then off to “blink” LEDs.
• Frees up the micro’s timer
• Continues to blink LEDs even when no longer connected to bus master
• Can be used to cycle relays and timers
• Higher frequency rate allows LEDs to be dimmed by varying the duty
cycle for Red/Green/Blue color mixing applications.
DesignCon 2003 TecForum I2C Bus Overview
127
Slide 127
These new devices are useful for LED driving and
blinking. The I2C/SMBus or the micro controller is not
40
AN10216-01 I2C Manual
I2C LED Blinkers and Dimmers
Frequency
Duty Cycle
0 (00H)
40 Hz
100 %
255 (FFH)
6.4 s
0.4 %
0 Input
0 0
0 0 0
Register(s)
Frequency
Duty Cycle
0 (00H)
160 Hz
0%
255 (FFH)
1.6 s
99.6 %
PWM0
256 - PWM 0
256
256
OFF
ON
160
256
0 PWM0
0 0 0
0
0
0
0 0 0
PSC0
0
OFF
0
0 PWM1
0 0 0
0
0
0
0
0
0 0Selector
0 0 0
LED
ON
PSC0 + 1
PSC0 + 1
PWM1
0
Blinkers
Dimmers
40
256 - PWM1
256
ON
PSC1 + 1
160
0 0 0
PSC1
I2C GPIO’s can be used to control LEDs in order to
visual status, like for example blink slowly when in
normal condition, blink faster in an alarm mode. The
main disadvantages of this method are the following:
• ON/OFF commands need to be sent all the time by
the master
• I2C bus can be tied by sending the ON/OFF
commands when a lot of LEDs needs to be
controlled
• At least one timer in the master needs to be
dedicated for this purpose
• Blinking is lost if the I2C bus hangs or if the master
fails
OFF
PSC1 + 1
40
ON
OFF ON
ON =
OFF =
ON,
ON, OFF, BR1, BR2
LED ON
LED OFF
DesignCon 2003 TecForum I2C Bus Overview
128
Slide 128
Using I2C for visual status
Slide 128 shows the register configuration of the LED
Blinkers and Dimmers.
• Products:
I2C Blinkers and Dimmers - Programming
• To program the 2 blinking rates
S
Address
W
A
PSC0
pointer
A
PSC0
A
PSC1
A
PWM1
A
PWM0
A
P
# of Outputs
2
4
8
16
Reset and POR
PCA9550
PCA9553
PCA9551
PCA9552
LED Blinkers
# of Outputs
2
4
8
16
Reset and POR
PCA9530
PCA9533
PCA9531
PCA9532
LED Dimmers
Blinking between 40 times a second to
once every 6.4 seconds
Blinking between 160 times a second to
once every 1.6 seconds.
Can be used for dimming/brightness or
PWM for stepper motor control
PSC0 pointer = 01H for 2, 4 and 8-bit devices
PSC0 pointer = 02H for the 16-bit devices
• To program the drivers
S
Address
W
A
LED SEL0
pointer
A
LEDSEL0
A
LEDSEL2
A
LEDSEL3
A
LEDSEL1
DesignCon 2003 TecForum I2C Bus Overview
A
P
Slide 131
LEDSEL0 pointer = 05H for 2, 4 and 8-bit devices
LEDSEL0 pointer = 06H for the 16-bit devices
I2C LED blinkers provide an elegant autonomous
solution:
• They have an built-in accurate oscillator requiring
no external components
• They can be programmed in one I2C access (2
selectable fully programmable blinking rates)
• Output state (Blinking rate 1, Blinking rate 2,
Permanently
ON,
Permanently
OFF)
is
programmed in one I2C access anytime.
Blinking is not lost, once the device is programmed, in
case the bus hangs or the master fails.
Only the 16-bit devices have 4 LED selector registers (8-bit devices have
2 registers, 2 and 4-bit devices have only one)
DesignCon 2003 TecForum I2C Bus Overview
129
Slide 129
Slide 129 shows the programming sequence for the
LED Dimmers and Blinkers.
Using I2C for visual status
• Use LEDs to give visual interpretation of a specific action:
– alarm status (using different blinking rates)
– battery charging status
• 1st approach: I2C GPIO’s
– Advantage:
– Simple programming
– Easy to implement
– Inconvenient:
– Need to continually send ON/OFF commands through I2C
– 1 microcontroller’s timer required to perform the task
– I2C bus can be tied up by commands if many LEDs to be controlled
– Blinking is lost if the I2C bus hangs
• 2nd approach: I2C LED Blinkers
– Advantage:
– One time programmable (frequency, duty cycle)
– Internal oscillator
– Easy to implement
– Device does not need I2C bus once programmed and turned on
DesignCon 2003 TecForum I2C Bus Overview
131
See Application Note AN264 for more information on
the LED Dimmers/Blinkers.
130
Slide 130
41
AN10216-01 I2C Manual
DIP Switch
I2C Dip Switches
I2C DIP Switches
I2C
Bus
MUX Select Pin
Write
Protect
Non MUX Output Pin
I2C Bus
Mux
EEPROM
Hardware Output
Pins
Hardware Input
Pins
• Non-volatile EEPROM retains values when the device is powered down
• Used for Speed Step™ notebook processor voltage changes when on
AC/battery power or when in deep sleep mode
• Also used as replacement for jumpers or DIP switches since there is no
requirement to open the equipment cabinet to modify the jumpers/DIP
switch settings
DesignCon 2003 TecForum
I2C
Bus Overview
I2C INTERFACE /
EEPROM Control
Mux
Select
Mode Selection
0
0EEPROM
0 0 00
0
0
0EEPROM
0 0 10
0
0
0EEPROM
0 0 20
0
0
0EEPROM
0 0 30
0
MUX
0HARDWARE
0 0 0 Value
0 0
PCA9561
6 Bits
DesignCon 2003 TecForum I2C Bus Overview
133
132
Slide 133
Slide 132
The PCA9561 shown in Slide 133 is unique in that it
has 6 hardware input pins and four internal 6-bit
EEPROM registers. Output selection is possible
between any one of these five 6-bit values at any time
via the I²C bus. The EEPROMs have a 10 year memory
retention and are rated for 3000 write cycles in the data
sheet but have been tested to 50,000 cycles with no
failures.
These devices were designed for use with Intel®
processors to implement the Speed Step™ technology
for notebook computers (selects different processor
voltages when connected to AC power, the battery or in
a deep sleep/deeper sleep mode), Dual BIOS selection
(select different operating systems during start-up).
Designers have however found other uses for these
devices such as; VGA/Tuner cards (select the
appropriate transmission standard), in inkjet printers
and are being used as replacement for jumpers or dip
switches since the I²C controlled integrated EEPROM
and Multiplexer eliminates the need to open equipment
to modify the settings by hand, making it easier to
change settings and less likely to damage the
equipment.
The hardware pins may not be used at all or may be
used for a default manufacturing address.
At
manufacturing, the I2C address of the targeted device
may be the one given by the default EEPROM values
(all Zero’s). If the customer wants to change the I2C
address, he has to Address the Multiplexed/Latched
EEPROM device (PCA8550, PCA9559, PCA9560 or
PCA9561) and program the EEPROM to the new value
they want.
I²C commands and/or hardware pins are used to select
between the default values or the setting programmed
from the I2C bus and stored in the onboard I2C
EEPROM register. These onboard values can be
changed at any time via the I²C bus. The non-volatile
I²C EEPROM register values stay resident even when
the device is powered down. The devices power up with
either the hardware pin inputs or the EEPROM0
register retained value on the hardware output pins
depending on the position (H or L) of the Mux select
pins.
If they use the PCA9560 or PCA9561, 2 or 4 different
values can be already pre-programmed. Put the right
logic level(s) on the Mux_select pin(s) if necessary (to
select the EEPROM values at the Mux input and
propagate them to the outputs (connected to the
Address pins of the targeted I2C device). Address the
targeted I2C device (programmed with the new I2C
address). Nice thing about using Multiplexed/Latched
EEPROM is that the configuration is not lost each time
supply is powered down.
The PCA9560 is footprint identical to the PCA9559 but
has two internal EEPROM registers to allow for three
preprogrammed setting (e.g., AC power/battery power,
deep sleep or deeper sleep mode).
42
AN10216-01 I2C Manual
•
•
I2C DIP Switches - PCA9561
• To program the 4 EEPROMS
S
Address
W
00H
A
A
EEPROM 0
A
EEPROM 2
EEPROM 3
A
EEPROM 1
A
A
A
P
Interrupt logic inputs for each channel and a combined
output are included on every multiplexer and provide a
flag to the master for system monitoring. These devices
do not isolate the capacitive loading on either side of
the device so the designer must take into account all
trace and device capacitance on both sides of the device
(any active channels). Pull up resistors must be used on
all channels.
• To read the 4 EEPROMS
S
Address
W
A
00H
A
EEPROM 1
A
S
Address
EEPROM 2
A
R
A
A
EEPROM 0
EEPROM 3
A
P
• To read the Hardware value
S
Address
W
A
FFH
A
S
FXH
A
P
Address
R
A
HW VALUE
A
P
•To select the mode
S
Address
W
A
DesignCon 2003 TecForum I2C Bus Overview
I2C sub-branch isolation
I2C bus level shifting (e.g., each individual
SCx/SDx channel can be operated at 1.8 V, 2.5 V,
3.3 V or 5.0 V if the device is powered at 2.5 V).
134
I2C Switches
Slide 134
Side 134 shows the typical program sequence for the
PCA9561. See Application Note AN250 for more
information on the DIP Switches.
I2C Bus
Reset
Interrupt Out
OFF
I2 C
Controller
OFF
I2C Bus 0
I2C Bus 1
Interrupt 0
Interrupt 1
Multiplexers and Switches
• Switches allow the master to communicate to one channel or multiple
I2C Multiplexers
downstream channels at a time
• Switches don’t isolate the bus capacitance
I2C Bus
OFF
I2 C
• Other Applications include: sub-branch isolation and I2C/SMBus level
Bus 0
shifting (1.8, 2.5, 3.3 or 5.0 V)
I2C Bus 1
Interrupt Out
I2 C
Controller
FEATURES
-Fan out main I2C/SMBus to multiple channels
-Select off or individual downstream channel
-I2C/SMBus commands used to select
channel
-Power On Reset (POR) opens all channels
-Interrupt logic provides flag to master for
system monitoring.
DesignCon 2003 TecForum I2C Bus Overview
Interrupt 0
Interrupt 1
Slide 136
KEY POINTS
-Many specialized devices have only one I2C
address and sometimes many are needed in the
same system.
-Multiplexers allow the master to communicate to
one downstream channel at a time but don’t
isolate the bus capacitance
-Other Applications include sub-branch isolation.
DesignCon 2003 TecForum I2C Bus Overview
136
The Switches allow multiplexing but also allow
multiple downstream channels to be active at the same
time that allows voltage level translation or load sharing
applications. The I2C SCL/SDA upstream channel to
fan out to multiple SCx/SDx channels that are selected
by the programmable control register. The Switches
can select individual SCx/SDx channels one at a time,
all at once or in any combination through I2C
commands and very primary designed for sub-branch
isolation and level shifting but also work fine for
address conflict resolution (Just make sure you do not
select two channels at the same time). Applications are
the same as for the multiplexers but since multiple
channels can be selected at the same time the switches
are really great for I2C bus level shifting (e.g.,
individual SCx/SDx channels at 1.8 V, 2.5 V, 3.3 V or
5.0 V if the device is powered at 2.5 V).
135
Slide 135
The multiplexer allows multiplexing multiple I2C
devices with the same I2C address. The I2C SCL/SDA
upstream channel to fan out to multiple SCx/SDx
channels that are selected by the programmable control
register. The I²C command is sent via the main I²C bus
and is used to select or deselect the downstream
channels. The Multiplexers can select none or only one
SCx/SDx channels at a time since they were designed
primarily for address conflict resolution such as when
multiple devices with the same I2C address need to be
attached to the same I2C bus and you can only talk to
one of the devices at a time.
A hardware reset pin has been added to all the switches.
It provides a means of resetting the bus should it hang
up, without rebooting the entire system and is very
useful in server applications where it is impractical to
reset the entire system when the I2C bus hangs up. The
switches reset to no channels selected.
These devices are used in video projectors and server
applications. Other applications include:
Address conflict resolution (e.g., SPD EEPROMs on
DIMMs).
43
AN10216-01 I2C Manual
Interrupt logic inputs and output are available on the
PCA9543 and PCA9545 and provide a flag to the
master for system monitoring. The PCA9546 is a lower
cost version of the PCA9545 without Interrupt Logic.
The PCA9548 provides eight channels and are more
convenient to use then dual 4 channel devices since the
device address does not have to shift.
The PCA9541/01 defaults to channel 0 on start up/reset.
The device was designed for a company that wanted the
device to connect master 0 to shared resources at start
up so they wouldn't have to send any commands.
The PCA9541/02 defaults to channel 0 on start up/reset
only after it has seen a stop command on bus 0. This is
our hot swap version, a requirement the company using
the PCA9541/01 didn't have (since they power down
the system before cards are inserted or removed). This
feature on the PCA9541/02 allows you to insert and
remove cards without confusing the slave devices on
the card by them being caught midway into an I2C
transmission if there is an active transmission on the
backplane/main bus.
These devices do not isolate the capacitive loading on
either side of the device so the designer must take into
account all trace and device capacitance on both sides
of the device (active channels only). Pull up resistors
must be used on all channels.
I2C Multiplexers & Switches Programming
The PCA9541/03 defaults to no channels selected on
start up/reset and one of the masters needs to command
the PCA9541/03 to select bus 0 or 1. We had some
customers interested in not connecting any bus until the
master was ready. This feature also allows the
PCA9541/03 to be used as a 'gatekeeper" multiplexer as
described in the data sheet specific applications section.
• To connect the upstream channel to the selected
downstream channel(s)
S
PCA954x
Address
W
A
CHANNEL
SELECTION
Selection is done at the
STOP command
P
A
• To access the downstream devices on the selected channel
S
Device
Address
W
A
Command
A
P
Once the downstream channel selection is done, there is no need to
access (Write) the PCA954x Multiplexer or Switch
The device will keep the configuration until a new configuration is
required (New Write operation on the PCA954x)
Master Selector in Multi-Point Application
DesignCon 2003 TecForum I2C Bus Overview
140
Master 1
PCA9541
PCA9541
PCA9541
PCA9541
PCA9541
PCA9541
PCA9541
PCA9541
Master 0
Slide 137
Slide 137 shows a typical programming sequence. See
Application Note AN262 for more information on the
switch/multiplexers.
I2C 2 to 1 Master Selector
Master 0 I2C Bus
Master 1 I2C Bus
Interrupt 0 Out
Interrupt 1 Out
DesignCon 2003 TecForum I2C Bus Overview
Slave Card
I2C Bus
I2 C
Interrupt In
Controller
Slide 139
Interrupt In
Reset
PCA9541 in a multi-point application were all cards use
the same two buses. Master 0 is the primary master and
master 1 is the back up master.
• Master Selector selects from two I2C/SMBus masters to a single channel
• I2C/SMBus commands used to select master
• Interrupt outputs report demultiplexer status
• Sends 9 clock pulses/stop to clear slaves prior to transferring master
DesignCon 2003 TecForum I2C Bus Overview
138
137
Slide 138
The PCA9541 is designed for applications where there
are two bus masters controlling the same slaves and the
masters need to be isolated for redundancy.
44
AN10216-01 I2C Manual
Bus Repeaters and Hubs
Master Selector in Point-Point Application
I2C Bus Repeater and Hub
Master 1
PCA9541
Master 0
400 pF
Master 1
Master 0
PCA9541
400 pF
SCL0
SCL1
SDA0
SDA1
400 pF
Enable
400 pF
400 pF
400 pF
400 pF
Master 1
Master 0
PCA9541
I2C Bus Repeater
5-Channel I2C Hub
PCA9515
PCA9516
Master 1
PCA9541
Master 0
• Bi-directional I2C drivers isolate the I2C bus capacitance to each segment.
• Multi-master capable (e.g., repeater transparent to bus arbitration and
contention protocols) with only one repeater delay between segments.
• Segments can be individually isolated
• Voltage Level Translation
• 3.3 V or 5 V voltage levels allowed on the segment
DesignCon 2003 TecForum I2C Bus Overview
139
DesignCon 2003 TecForum I2C Bus Overview
142
Slide 140
Slide 142
PCA9541 in a point to point application where there are
two dedicated buses to each slave card for even higher
redundancy, such as a bent pin would not disable all the
cards.
These bi-directional I2C drivers enable designers to
isolate the I2C bus capacitance into smaller sections,
accommodating more I2C devices or a longer bus
length. The I2C specification only allows 400 pF load
on the I2C bus and these devices can break the I2C bus
into multiple 400 pF segments.
Voltage Level Translators
I2C Bus Bi-Directional Voltage Level Translation
GTL2002
200 KΩ
1.5 V
1.2 V
PCA9515 and PCA9516 applications include
supporting the PCI management bus, > 8 PCI slots,
isolating SMBus to hot plug PCI slots and driving I2C
to multiple system boards. Either 3.3 V or 5 V voltages
are allowed on each segment to allow devices with
different voltages ranges to be used on the same bus.
The devices are transparent to bus arbitration and
contention protocols in a multi-master environment.
5V
1.8 V
1.0 V
VCORE
CPU I/O
GND
GREF
SREF DREF
S1
D1
S2
D2
VCC
Chipset I/O
•
•
•
•
Voltage translation between any voltage from 1.0 V to 5.0 V
Bi-directional with no direction pin
Reference voltage clamps the input voltage with low propagation delay
Used for bi-directional translation of I2C buses at 3.3 V and/or 5 V to
the processor I2C port at 1.2 V or 1.5 V or any voltage in-between
• BiCMOS process provides excellent ESD performance
DesignCon 2003 TecForum I2C Bus Overview
The PCA9518 expandable hub is designed to allow
more multiple groups of 4 downstream channels.
Hot Swap Bus Buffers
141
Slide 141
I2C Hot Swap Bus Buffer
These devices are very useful in translation of I2C bus
voltages as a lower and lower core voltages are used.
The GTL2000 is 22 bits wide, the GTL2002 is 2 bits
wide and the GTL2010 is 10 bits wide. See Application
Note AN10145 for more information.
PCA9511
PCA9512
PCA9513
PCA9514
SCL
SDA
• Allows I/O card insertion into a live backplane without corruption of busses
• Control circuitry connects card after stop bit or idle occurs on the backplane
• Bi-directional buffering isolates capacitance, allows 400 pF on either side
• Rise time accelerator allows use of weaker DC pull-up currents while still
meeting rise time requirements
• SDA and SCL lines are precharged to 1V, minimizing current required to
charge chip parasitic capacitance
DesignCon 2003 TecForum I2C Bus Overview
Slide 143
45
143
AN10216-01 I2C Manual
The PCA9511 hot swappable 2-wire bus buffer allows
I/O card insertion into a live backplane without
corruption of the data and clock busses. Control
circuitry prevents the backplane from being connected
to the card until a stop bit or bus idle occurs on the
backplane without bus contention on the card. When
the connection is made, the PCA9511 provides bidirectional buffering, keeping the backplane and card
capacitances isolated. Rise time accelerator circuitry
allows the use of weaker DC pull-up currents while still
meeting rise time requirements.
product’s internal I2C bus, will require safety
isolation.
Medical equipment requires safety isolation of the
patient connections. Any power for the isolated
circuitry must be passed via isolating transformers.
The data paths are sometimes transformer coupled
using carrier tones, but they could also be via optoisolated I2C.
Lamp dimmers and switches can be controlled over
I2C data links.
Each light in a disco or live stage production could
have its own identity and be individually computer
controlled from a control desk or computer via I2C.
Dimming (phase control) can be done with small
micros or TCA280B from IES. Putting the phase
controller inside each lamp will make it easier to
meet EMC rules - lower power wiring radiation.
•
•
•
During insertion, the SDA and SCL lines are
precharged to 1 V to minimize the current required to
charge the parasitic capacitance of the chip.
The PCA9511 incorporates a digital ENABLE input
pin, which forces the part into a low current mode when
asserted low, and an open drain READY output pin,
which indicates that the backplane and card sides are
connected together.
Applications requiring extension of the I2C bus (both
P82B715 and P82B96):
• Almost any application where a remote control
needs to be located some distance from the main
equipment cabinet, e.g. in medical or industrial
applications. Some safe distances the P82B715 or
P82B96 can transmit I2C signals are:
o P82B715: 50 Ω coax cable or twistedpair cables - 50 meters, 85 kHz
o P82B96: Telephone cable pairs or Flat
Ribbon Cable - 100 meters at 71 kHz or 1
kilometer at 31 kHz
The PCA9512/13/14 are variants on the PCA9511.
The PCA9511DP is an alternate source for the Linear
Tech LTC4300-1I and the PCA9512DP is an alternate
source for the Linear Tech LTC4300-2I.
Bus Extenders
I2C Bus Extenders
Changing I2C bus signals for multi-point applications
3.3/5V
12V
12V
Twisted-pair telephone wires,
USB or flat ribbon cables
Up to 15V logic levels, Include VCC & GND
SCL
Note: Schottky
diode or Zener
clamps may be
needed to limit
spurious signals on
very long wiring
I2C
Bus Extender
P82B715
NO LIMIT to the number of
connected bus devices !
12V
3.3/5
3.3V
SDA
KEY POINTS
High drive outputs are used to extend
the reach of the I2C bus and exceed
the 400 pF/system limit.
Possible distances range from 50
meters at 85kHz to 1km at 31kHz over
twisted-pair phone cable.
Bus Buffer has split high drive outputs
allowing differential transmission or
Dual Bi-Directional Bus Buffer
Opto-isolation of the I2C Bus.
P82B96
Link parking meters
and pay stations
DesignCon 2003 TecForum I2C Bus Overview
P82B96
P82B96
SDA/SCL
SDA/SCL
SDA/SCL
Link vending machines
to save cell phone links
•-•-•-•-•--
P82B96
P82B96
•-•-•-•-•--
•-•-•-•-•--
P82B96
SCL
SDA
Warehouse
pick/pack
systems
• Factory automation
• Access/alarm systems
• Video, LCD & LED display signs
• Hotel/motel management systems
• Monitor emergency lighting/exit signs
144
DesignCon 2003 TecForum I2C Bus Overview
145
Slide 144
Slide 145
Applications requiring opto-isolation of the I2C bus
(P82B96 only):
• Digital telephone answering machines (Philips
PCD6001), Fax machines, feature phones and
security system auto-dialers are connected to the
phone line and often powered from the 110/230 V
mains via double-insulated ‘plug-pack’ DC power
packs.
Many use Microcontrollers (e.g.
PCD33xx), and some will already have I2C buses.
Any other interfaces, e.g. connecting to the
The buffered 12V bus has exactly the same multi-drop
characteristic as a standard I2C but the restriction to 400
pF has been removed so there is no longer any
restriction on the number of connected devices. P82B96
alone can sink at least 30 mA (static specification, > 60
mA dynamic) and there is no theoretical limitation to
providing further amplification. Just adding a simple
2N2907A emitter-follower enables 500 mA bus sink
capability.
46
AN10216-01 I2C Manual
Just adding a simple 2N2907A emitter-follower enables
500 mA sink capability.
With large sink currents it is possible to drive a special
type of low impedance “I2C” bus - say at 500 Ω, or
even down to 50 Ω. With the ability to use logic
voltages up to 15 V it is possible to drive hundreds of
meters of cable, providing the clock rate is decreased to
allow time for the signals to travel the long distances.
It’s possible to run 100 meters with at least 70 kHz and
1kilometer at 30 kHz. That beats CAN bus, based on
useful byte rate!
This allows longer distance communication on the I2C
bus. See Application Note AN255 for more
information.
Electro-Optical Isolation
Changing I2C bus signals for Opto-isolation
3.3/5V
Note the special bus formed when the P82B96 Tx and
Rx outputs are linked has all the usual properties of an
I2C bus -- it IS an I2C bus, but with some of the
limitations removed. So it is a ‘multi-drop’ bus that can
support ANY NUMBER of physical connection nodes.
Of course the method of addressing of individual nodes
must be designed but it’s easy with microcontrollers,
and possible using hardware, to achieve sub-addressing.
SCL
P82B96
SDA
SDA
Bi-directional
data streams
Special logic levels
( I2C compatible 5V)
I2C currents (3mA)
Low cost Optos can
be directly driven
(10-30mA)
VCC 1 = 2 to 12V
Higher current option,
up to 30mA static sink
4N36 Optos for ~5kHz
6N137 for 100kHz
Re-combined to I2C
I2C compatible levels
HCPL-060L for 400 kHz e.g. Vcc 2 = 5V
Controlling equipment on phone lines
AC Mains switches, lamp dimmers
Isolating medical equipment
DesignCon 2003 TecForum I2C Bus Overview
147
Slide 147
Here the 30mA drive capability at Tx is used to directly
drive low cost opto-couplers to achieve isolation of the
I2C bus signals. This allows I2C nodes in industrial
applications (e.g. factory automation) to have their
grounds at different potentials. It allows I2C chips
inside telephones to interface to external devices that
need to be grounded, for example to a PC to log Faxed
information. It allows driving I2C chips connected to
the AC power mains with a safety isolation barrier. The
P82B96 allows operation up to 400 kHz.
Changing I2C bus signals for driving long distances
Remote Control
Enclosure
12V
Vcc 2
SCL
3.3/5V
Application examples: Parking meters and vehicle
sensors are linked to a pay station, some have credit
card and pay-by-phone options. Groups of vending
machines can be linked so only one in a group needs a
cell phone link for payment facility or reporting the
stock/sales/faults situation. Warehouse systems transmit
requirements to workstations, print labels, have realtime visibility of work status. Motel systems control
access, air-con, messages via teletext on TV screen,
report room status.
3.3 -5V
Vcc 1
12V
Long cables
SCL
12V
3.3-5V
Rise Time Accelerators
SDA
P82B96
P82B96
Bi-directional
data streams
Special logic levels
(I2C compatible 5V)
Simply link the pins
for Bi-directional
data streams
2V through 12V logic levels
Conventional CMOS
logic levels (2-15V)
Able to send VCC and GND
Higher current option,
up to 30mA static sink
100 meters at 70kHz
NO LIMIT to the number of
connected devices !
I2C currents (3mA)
Rise Time Accelerators
Twisted-pair telephone wires, Re-combine to
bi-directional I2C
USB or flat ribbon cables
DesignCon 2003 TecForum I2C Bus Overview
Convert the logic
signal levels back
to I2C compatible
The LTC®1694-1 is a dual SMBus active pullup designed to enhance data transmission
speed and reliability under all specified SMBus
loading conditions. The LTC1694-1 is also
compatible with the Philips I2C Bus.
Hot Swap
Protection
146
The LTC1694-1allows multiple device connections or a longer, more
capacitive interconnect, without compromising slew rates or bus
performance, by supplying a high pull-up current of 2.2 mA to slew the
SMBus or I2C lines during positive bus transitions
Slide 146
During negative transitions or steady DC levels, the LTC1694-1 sources
zero current. External resistors, one on each bus line, trigger the
LTC1694-1 during positive bus transitions and set the pull-down current
level. These resistors determine the slew rate during negative bus
transitions and the logic low DC level.
It is allowed to simply join the two unidirectional logic
pins Tx and Rx to form a bi-directional bus with all the
same features as I2C but with freedom to choose
different logic voltages and sink larger currents than the
3 mA limitation of the I2C specifications.
P82B96 alone can sink at least 30 mA (static
specification, >60 mA dynamic) and there is no
theoretical limitation to providing further amplification.
DesignCon 2003 TecForum I2C Bus Overview
148
Slide 148
Rise time accelerators like the LTC1694 and LCT16941 are used to help control the rise time of the I2C bus.
47
AN10216-01 I2C Manual
See Application Note AN255 Appendix 6 for
differences between the LTC1694 and LCT1694-1.
Digital Potentiometers
Digital Potentiometers
Parallel Bus to I2C Bus Controller
• DS1846 nonvolatile (NV) tripotentiometer, memory, and
MicroMonitor. The DS1846 is a highly
integrated chip that combines three
linear-taper potentiometers, 256 bytes of
EEPROM memory, and a MicroMonitor.
The part communicates over the
industry-standard 2-wire interface and is
available in a 20-pin TSSOP.
I2C Interface
I2C Bus
Chip Enable
Write Strobe
Read Strobe
Reset
Address Inputs
Interrupt Request
Data (8-bits)
Operation
Control
Control
Bus Buffer
Microcontroller
Parallel Bus to I2C Bus Controller
• The DS1846 is optimized for use in a variety of embedded systems
where microprocessor supervisory, NV storage, and control of analog
functions are required. Common applications include gigabit
transceiver modules, portable instrumentation, PDAs, cell phones, and
a variety of personal multimedia products.
• Controls all the I2C bus specific sequences, protocol, arbitration and
timing
• Serves as an interface between most standard parallel-bus
microcontrollers/ microprocessors and the serial I2C bus.
• Allows the parallel bus system to communicate with the I2C bus
DesignCon 2003 TecForum I2C Bus Overview
DesignCon 2003 TecForum I2C Bus Overview
Slide 150
149
Digital potentiometers are similar to the potentiometers
you used to adjust with the screwdriver but these are
adjusted via the I2C bus. Some digital potentiometers
include onboard EEPROM so that settings are retained
with the device is powered down.
Slide 149
The PCF8584 and PCA9564 serve as an interface
between most standard parallel-bus microcontrollers/
microprocessors and the serial I2C bus and allow the
parallel bus system to communicate bi-directionally
with the I2C bus. This commonly is referred as the bus
master. Communication with the I2C bus is carried out
on a byte-wise basis using interrupt or polled
handshake. It controls all the I2C bus specific
sequences, protocol, arbitration and timing.
Analog to Digital Converters
Analog to Digital Converter
Supply
INT
The PCA9564 is similar to the PCF8584 but operates at
2.3 to 3.6 V VCC and up to 400 kHz (slave mode) with
various enhancements added that were requested by
engineers.
1. Voltage range
2. Max I2C freq.
3. Clock source
flexible
4. Parallel interface
processors
150
PCA9564
2.3-3.6V
360 kHz
Internal
PCF8584
4.5-5.5V
90 kHz
External
Comments
PCA9564 is 5V tolerant
Faster I2C
Less expensive/more
Fast
Slow
Compatible with faster
SDA
SCL
POR
+
Oscillator, intern /
extern
+
Interrupt
I2C-bus
interface
+
ADC /
DAC
+
+
Sub
address
decoder
+
Analog
reference
• 4 channel Analog to Digital
• 1 channel Digital to Analog
DesignCon 2003 TecForum I2C Bus Overview
These devices translate between
digital information communicated
via the I2C bus and analog
information measured by a
voltage.
Analog to digital conversion is
used for measurement of the
size of a physical quantity
(temperature, pressure …),
proportional control or
transformation of physical
amplitudes into numerical values
for calculation.
Digital to analog conversion is
used for creation of particular
control voltages to control DC
motors or LCD contrast.
151
Slide 151
In addition, the PCA9564 has been made very similar to
the Philips standard 80C51 microcontroller I2C
hardware so existing code can be utilized with a few
modifications.
The PCF8591 is capable of converting four different
analog voltages to the digital values for processing in
the microcontroller. It can also generate one analog
voltage by converting an 8-bit digital value provided by
the microcontroller.
Several kinds of analog information in your
applications, such as temperature, pressure, battery
level, signal strength, etc can be processed by such a
device. These are digitally processed and can be
subsequently displayed, used to control contacts,
switches, relay, etc. for example using the previously
discussed I/O expander PCA9554. The D/A output is
useful for such jobs as LCD contrast control.
48
AN10216-01 I2C Manual
2 is identical to the PCF85102C-2 except that the fixed
I2C address is different, allowing up to eight of each
device to be used on the same I2C bus.
Serial RAM/EEPROM
I2C Serial CMOS RAM/EEPROMs
EEPROM
Standard Sizes
RAM
128 x 8-byte (1 kbit)
256 x 8-byte (2 kbit)
512 x 8-byte (4 kbit)
1024 x 8-byte (8 kbit)
2048 x 8-byte (16 kbit)
4096 x 8-byte (32 kbit)
8192 x 8-byte (64 kbit)
16384 x 8-byte (128 kbit)
32768 x 8-byte (256 kbit)
65536 x 8-byte (512 kbit)
24C01
24C02
24C04
24C08
24C16
24C32
24C64
24C128
24C256
24C512
Address
pointer
POR
Supply
Hardware Monitors/Temp & Voltage Sensors
SDA
Address
pointer
256
Byte
RAM
POR
I2C-bus
interface
SCL
256
I2C-bus
Byte
Sub address
interface
Sub
decoder
E2PROM
address
decoder
Sub
address
decoder
I2C Hardware Monitors
Remote
Sensor
Digital Temperature
• I²C bus is used to read and write information to and from the memory
• Electrically Erasable Programmable Read Only Memory
• 1,000,000 write cycles, unlimited read cycles
• 10 year data retention
Watchdog™
I2C Temperature and Voltage
NE1617A
LM75A
Monitor(Heceta4)
NE1618
NE1619
153
– Sense temperature and/or monitor voltage via I²C
– Remote sensor can be internal to microprocessor
Slide 153
There are different kinds of memories in the line of I²C
bus compatible components such as: RAM, EEPROM,
video memories and Flash memories.
• RAM is Random Access Memory
• EEPROM is Electrically Erasable Programmable
Read Only Memory
• Common small serial memories (RAM and
EEPROM) are often used in applications.
EEPROMs are particularly useful in applications
where data retention during power-off is essential
(for example: meter readings, electronic key,
product identification number, etc).
• A single pinning is used for these ICs because they
are very similar and their pinouts have been
intentionally designed for interchangeability.
• EEPROMs store data (2kbits organized in 256 x 8
in the PCF8582C-2 for example), including set
points, temperature, alarms, and more, for a
guaranteed minimum storage time of ten years in
the absence of power. EEPROMs change values
100,000 to 1,000,000 times and have an infinite
number of read cycles, while consuming only 10
micro amperes of current.
DesignCon 2003 TecForum I2C Bus Overview
154
Slide 154
Hardware monitors such as the NE1617A, NE1618,
NE1619 and LM75A use the I²C bus to report
temperature and/or voltage. Some of the temperature
monitors include hardware pins that allow external
transistors/diodes to be located in external components
(e.g., processors) that sense the temperature much more
accurately then if the sensor was mounted externally on
the package. The test pins are used at the factory to
calibrate/set the temperature sensor and are left floating
by the customer.
Microcontrollers
Analog
Comparators
Ports
0, 1, 2, 3
600% Accelerated C51 Core
Keypad/
Pattern Match
Interrupt
For example, the PCA8581 is organized as 128 words
of 8-bytes. Addresses and data are transferred serially
via a two-line bi-directional bus (I2C bus). The built-in
word address register is incremented automatically after
each data byte is written or read. All bytes can be read
in a single addressing operation. Up to 8 bytes can be
written in one operation, reducing the total write time
per byte.
Internal ±2.5%
7.3728 MHz
RC Oscillator
8K ISP
512B
768B
IAP
Data
SRAM
Flash EEPROM
Timer
0/1
16-bit
Power Management, RTC, WDT,
power-on-reset, brownout detect
32xPLL
−
+
I2C Microcontroller
+
Bus Overview
I2C Temperature Monitor
−
DesignCon 2003 TecForum
I2C
Sensor and Thermal
16-bit
PWM CCU
Enh.
UART
I2C
SPI
Microcontrollers with Multiple Serial ports can
convert from:
I2C to UART/RS232 – LPC76x, 89C66x and
89LPC9xx
I2C to SPI - P87C51MX and 89LPC9xx family
I2C to CAN - 8 bit P87C591 and 16 bit PXA-C37
DesignCon 2003 TecForum I2C Bus Overview
The master can be either a
bus controller or µcontroller
and provides the brains
behind the I2C bus operation.
A bus controller adds I2C bus
capability to a regular
µcontroller without I2C, or to
add more I2C ports to
µcontrollers already
equipped with an I2C port
such as the:
P87LPC76x
100 kHz I2C
P89C55x
100 kHz I2C
P89C65x
100 kHz I2C
P89C66x
100 kHz I2C
P89LPC932
400 kHz I2C
155
Slide 155
The PCA8582C-2 is pin and address compatible to:
PCF8570, PCF8571, PCF8572 and PCF8581. The
PCF85102C-2 is identical to the PCF8582C-2 with pin
7 (Programming time control output) as a ‘no connect’
to allow it to be used in competitors sockets since PTC
should be left floating or held at VCC. The PCF85103C-
Microcontrollers are the brains behind the I2C bus
operation. More and more micros include at least one
I2C port if not more to allow multiple I2C buses to be
controlled from the same microcontroller.
49
AN10216-01 I2C Manual
I2C Patent and Legal Information
whatever. This also applies to FPGAs. However, since
the FPGAs are programmed by the user, the user is
considered a company that builds an I2C-IC and would
need to obtain the license from Philips.
The I2C bus is protected by patents held by Philips.
Licensed IC manufacturers that sell devices
incorporating the technology already have secured the
rights to use these devices, relieving the burden from
the purchaser. A license is required for implementing
an I2C interface on a chip (IC, ASIC, FPGA, etc).
Apply for a license or text of the Philips I2C Standard
License Agreement
• US and Canadian companies: contact Mr.
Piotrowski (pc.mb.svl@philips.com)
• All other companies: contact Mr. Hesselmann
(pc.mb.svl@philips.com)
It is Philips's position that all chips that can talk to the
I2C bus must be licensed. It does not matter how this
interface is implemented. The licensed manufacturer
may use its own know how, purchased IP cores, or
ADDITIONAL INFORMATION
The latest datasheets for both released and sampling general purpose I2C devices and other Specialty Logic products can
be found at the Philips Logic Product Group website: http://www.philipslogic.com/i2c
Datasheets for all released Philips Semiconductors I2C devices can be found at the Philips Semiconductors website:
http://www.semiconductors.philips.com/i2c
More information or technical support on I2C devices can be provided by e-mail: pc.mb.svl@philips.com
APPLICATION NOTES
AN168
Theory and Practical Consideration using PCF84Cxx and PCD33xx Microcontrollers
AN250
PCA8550 4-Bit Multiplexed/1-Bit Latched 5-Bit I2C E2PROM
AN255
I2C/SMBus Repeaters, Hubs, and Expanders
AN256
PCA9500/01 Provides Simple Card Maintenance and Control Using I2C
AN262
PCA954X Family OF I2C/SMBus Multiplexers and Switches
AN264
I2C Devices for LED Display Control
AN444
Using the P82B715 I2C Extender on Long Cables
AN460
Using the P82B96 for Bus Interface
AN469
I2C I/O Ports
AN10145
Bi-directional Low Voltage Translators GTL2000, GTL2002, GTL2010
AN10146
I2C 2002-1 Evaluation Board
AN95068
C Routines for the PCx8584
AN96119
I2C with the XA-G3
AN97055
Bi-Directional Level Shifter for I2C-Bus and Other Systems
ANP82B96
Introducing the P82B96 I2C Bus Buffer
50
AN10216-01 I2C Manual
ANZ96003
Using the PCF8584 with Non-Specified Timings and Other Frequently Asked Questions
51
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