User's manual, JED AVR595 SBC using Atmel's ATmega2561

User's manual, JED AVR595 SBC using Atmel's ATmega2561
User’s manual, JED AVR595 SBC using Atmel’s ATmega2561
(Luke De Vincentis, Dec 2nd 2010)
The AVR595 board is a small form factor, general-purpose SBC from JED. It has been designed specifically with fieldbased low power data logging applications in mind. It has a powerful 8 bit AVR CPU and features a highly accurate
RTC, loads of onboard flash memory, very high resolution 24 bit ADC, direct LCD and keypad support as well as
multiple digital/analog CPU inputs and a number of high current sinking FET driven outputs. If you are looking for a
compact, highly versatile, industrial strength SBC then the AVR595 is a great choice!
At the heart of the AVR595 is the ATmega2561 CPU from Atmel. It features the standard ATmega core CPU with 8K
RAM, 256K FLASH and 4K of EEPROM all in a 64 pin package. It has 2 serial UARTs, I2C and SPI interfaces, and 54
I/O lines. The full device data-sheet is 449 pages long, and is available at:
http://www.atmel.com/dyn/products/product_card.asp?family_id=607&family_name=AVR+8%2DBit+RISC+&part_id
=3632
This manual provides a basic quick start information guide followed by a comprehensive step by step tour of the
AVR595 schematic covering all board functions.
In the following manual notes, reference is made repeatedly to CPU functions accessed by port number, and the easiest
way to find out what is inside the CPU “behind” the pins connected to the outside world on the AVR595 board is
simply to open the Atmega2561 data sheet and use the CTRL F (Find) function to search the PDF data sheet by port
number in the CPU data. (The format used for port addresses is “PB3” for Port B, bit 3, in both this manual, in the
Atmel data sheet, in the JED schematic diagrams, so all documents are searchable with the same “P/letter/bit-number”
format in the search.)
JED AVR595 User’s Manual (Dec 2nd 2010 © JED Microprocessors Pty Ltd)
Page 1
Quickstart Guide
J7
J14
J4
J13
J6
J12
J8
J9
J10
J2
To get up and running with the AVR595 board, on J2 link the ‘IGN SWITCH’ input to the ‘Power In’ terminal then
apply 6.5-30v DC to the ‘POWER IN and ‘GND’ terminals. The board comes loaded with a demo C program which
displays a test menu on a terminal running at 9600 baud (8,N,1) via RS232 0 on J6. This demo program allows the user
to test all functions on the board. Un-programmed the board draws under 30mA in quiescent current.
JED AVR595 User’s Manual (Dec 2nd 2010 © JED Microprocessors Pty Ltd)
Page 2
A WALK THROUGH THE SCHEMATIC, FUNCTION BY FUNCTION, PAGE BY PAGE ..4
CPU basics, Power Supply, Voltage Reference (Schematic sheet 1)............................................................................. 4
LCD display and DIP Switch (Schematic Sheet 2)......................................................................................................... 5
Keyboard, DIP switch, IO expansion (Schematic Sheet 3)............................................................................................ 5
RS232 Ser0 and Ser1, RS485, V-Drive (Schematic Sheet 4) ......................................................................................... 6
I2C, RTC and memory (Schematic Sheet 5) ................................................................................................................... 6
Eight Analog or Digital Inputs and Delta-Sigma ADC (Schematic sheet 6) ................................................................ 7
Eight FET Outputs, 1-Wire and External Interrupts (Schematic sheet 7) .................................................................. 8
CPU FLASH programming/re-programming................................................................................................................ 8
AVR programming languages. ........................................................................................................................................ 9
JED AVR595 User’s Manual (Dec 2nd 2010 © JED Microprocessors Pty Ltd)
Page 3
A walk through the schematic, function by function, page by page.
CPU basics, Power Supply, Voltage Reference (Schematic sheet 1)
On Sheet 1 the CPU power and oscillators are covered.
Crystal
XTAL1 is normally a 3.6864 Mhz, but is deliberately NOT surface mounted so JED or users can change this to any
frequency up to 16.0 Mhz. This is loaded as the default CPU clock source.
Oscillator
The LTC6930 is a high precision, low power oscillator from Linear Tech. This can be loaded as an alternative to the
standard crystal for a high precision, ultra low power 3.6864 Mhz CPU clock source.
See: http://cds.linear.com/docs/Datasheet/6930fb.pdf
CPU Digital power and Analog power
Power is provided to the CPU via EMC filtering inductors LC2 and LC1. Many bypass capacitors, a mix of low ESR
Tantalum and ceramic, are used to bypass all the power pins and the voltage reference to the ground plane on an inner
layer of the board.
Voltage reference
An accurate, 4.096 volt reference (U2, Linear Tech LT1790ACS6-4.096,) feeds the CPU’s AREF pin 62. This part
does not need trimming, as it has a basic accuracy of 0.05% and a drift less than 10ppm/deg. C over the full industrial
temperature range.
In a vehicle-based application, the board runs from 12 volt (“always on”) vehicle power, and is transient protected with
a polyfuse and transorb for load-dump or reverse polarity and filtered. (This filtered power is available on a screw
terminal to run off-board equipment, eg a modem or radio. The filtering can be extended off-board, or an external Li
battery or NiMH battery backup with charger can also be linked in here.
Power can be switched on by the RTC alarm using the RTC interrupt output. The board will run from as low as 6.5
volts, but is fully protected for load dump and transients or reverse voltages for 12 volt automotive applications.
A Recom switching regulator with a 6.5 to 34 volt input range and 5 volts out at 0.5A (18v max) is used as the main
onboard 5volt supply. The 5 volt main switching regulator can also power the LCD backlight, if used.
(See: http://www.recom-international.com/pdf/innoline/R-78xx-0.5.pdf )
Vcc at 5.0 volts is available to outside devices on J14.6 (or this board could have no regulators, and be powered
completely from external regulators or a battery-backed power system can feed into these terminals, in low power
logger applications.)
Vcc at 3.3V volts is regulated on board with a small linear regulator to run the DataFlash.
The power supply control and regulator components provide the following:
•
Low-power application suited (eg a vehicle-based data logger), it has a 12 volt “ignition” sense input which powers
up a system when the vehicle key is turned. Once the board is powered up, CPU “Hold on” signal via PB4 allows
the board to remain powered up once ignition signal is removed.
•
“Vin-switched” is available on a screw terminal on J2.2 to power off-board radio/modems.
In a battery-powered and/or solar-powered data logging system, the user can either run the CPU all the time and power
it down internally with the flexible power control register, or close the CPU down and have the RTC power it up at
regular intervals.
JED AVR595 User’s Manual (Dec 2nd 2010 © JED Microprocessors Pty Ltd)
Page 4
LCD display and DIP Switch (Schematic Sheet 2)
Port C is pinned out to J15 for the LCD. The LCD can be a 4 by 20, a 2 by 40 or a 4 by 40 text display (using two
enable lines). The LCD text display connects to J15. This connector matches to pin order of common HM44780 display
pinouts, and the port C pins PC4 … 7 connect to the LCD display’s D4 … 7 data lines. The display is used in “nibble”
mode with two 4-bit transfers per byte, as is provided by all compiler LCD drivers. Port PC0 is the Register Select pin,
PC1 is R/W*, and PC2 is the first LCD E1 (enable) pin. PB7 provides LCD bias control via PWM output OC1C.
A flexible backlight powering system is provided, which allows the CPU to control the power on/off for the LCD
backlight. An N-channel power FET, F8 is controlled by port PC3, and this grounds the –ve end of the backlight LED
array. The positive end of the LED array is fed to Vcc.
Keyboard, DIP switch, IO expansion (Schematic Sheet 3)
Keyboard
Located on J3 this can be a 4 by 4 matrix or 8 individual switches to a ground pin on the keyboard connector. The user
can configure the keyboard style by controlling the data direction registers associated with the ports PA0 … PA7.
Software in a number of compilers can automatically scan at least a 4 x 4 keyboard on one port (Port A’s 8 pins, 4 as
inputs and 4 as outputs).
Alternatively an 8 way DIP switch is also provided for use on Port A as a general purpose onboard user input to select
various operating modes etc.
The ATmega2560 CPU includes a powerful hardware implementation of “SPI”, a high-speed clocked synchronous
communications protocol (also compatible also with National’s Microwire). Lines MOSI (Master Out Slave In), SCK
(clock) and MISO (Master In Slave Out) use in turn CPU port bits PB2, PB1 and PB3. Each device communicating
with the CPU via SPI needs a CPU pin allocated as a LOW true chip select.
As well, the SPI system on this board is used to communicate with the on-board DataFlash memory (using port PG5 as
the low-true chip select)
CPU Flash programming
The USART0 system and SPI clock is used for CPU FLASH memory programming, and J1, a 6-pin connector on the
board has the first six pins allocated to device programming, in a way compatible with Atmel’s ISP programmer’s 6-pin
ribbon cable connector. Ground, 5volt Vcc and RESET* lines are on this connector as well. (See:
http://www.atmel.com/dyn/products/tools_card.asp?family_id=607&family_name=AVR+8%2DBit+RISC+&tool_id=3
808 )
JED AVR595 User’s Manual (Dec 2nd 2010 © JED Microprocessors Pty Ltd)
Page 5
RS232 Ser0 and Ser1, RS485, V-Drive (Schematic Sheet 4)
The two serial interfaces are interfaced to RS232 user lines with a RS232 transceiver MAX 3224ECUP, U8.
Serial0 interface TX0/RX0 is available on J6. Ser0 is multiplexed with the V-Drive via U9. The control pin for this is
USB_ON (CPU pin PG3) which at logic high selects SER0 and at logic low selects the V-drive and supplies power to it
via F6.
Serial1 interface TX1/RX1 is available on J4. Ser1 is also shared with the RS485/TTL option via jumpers on L1. An
LTC485 tranceiver may also be loaded upon request to provide half duplex RS485 communications via J7. The Tx
enable is available externally via J7.2 or under CPU control via pin PGO. As standard the Ser1 option features the TTL
configuration with link resistors in R22 and R23 in place of the RS485 transceiver for TTL signals for direct connection
to a radio/modem. J7.1 also provides a switched 5v filtered power output for powering an external radio, modem etc.
This may be controlled via the RADIO_ON signal on pin PG1.
Jumper settings for Ser1 are as follows:
RS232
RS485/TTL
Link L1 1-3, 2-4
Link L1 3-5, 4-6
V-Drive USB
A USB memory stick interface option is available for logging/file transfer, via a VDRIVE2 USB host system which can
be mounted on a bracket accessible externally. A flying cable connects from the USB host card to the main CPU card
via 2mm header J5. A serial port connects to the interface at CMOS levels, and both devices have simple ASCII or
binary serial commands. Files can be created, opened, read or written and directories can be created or deleted. Files on
the USB stick are compatible with FAT file systems for Windows/DOS systems.
(See: http://www.ghielectronics.com/details.php?id=1&sid=3
and http://www.ftdichip.com/Support/Documents/DataSheets/Modules/DS_VDRIVE2.pdf)
Upon request there is a separate document available from JED which details the initialization sequence and command
set for the V-Drive.
I2C, RTC and memory (Schematic Sheet 5)
I2C expansion system
The ATmega2561 CPU includes a full hardware implementation of the I2C communications system for expanding
applications hardware to other chips, either on-board or off-board. (Atmel calls it the TWI or Two Wire Interface).
On the AVR595 board, the I2C interface is used to communicate with the Real Time Clock (DS3232), and the FRAM
non-volatile device (FM24C256).
The interface is available on J11, a 4-pin header for expansion off-board. This header includes a 5volt Vcc pin and
ground pin, as well as the SDA and SDL signal lines which are both pulled up to Vcc via 2k7 resistors. The interface is
non-buffered, and the pinout is compatible with a range of I2C expansion boards designed by JED in connection with
the AVR200 project board. (see: http://www.jedmicro.com.au/avr200.htm ) Interface boards available include eight
FET outputs, eight logic inputs, an LCD interface to a range of displays, and a 4 x 4 keyboard scanner.
DS3231 Real Time Clock, Battery backed RAM and Temperature transducer
The DS3232 provides a Real-Time-Clock to the AVR595 system. It runs from the I2C bus, and as well as very accurate
time and calendar functions, it provides an alarm capable of automatically powering up a sleeping system. The
timekeeping functions and the RAM are battery backed by a rechargeable, lithium cell held in a secure, vertical battery
holder. The 32Khz crystal is inside the moulded package, protecting it from mechanical damage and effects from
electrical or mechanical noise to the high-impedance crystal pins, which are now completely internal.
This RTC device uses a temperature-compensated crystal oscillator (TXCO) to provide a time-keeping accuracy of +/2ppm from 0 to 40 degrees C and +/- 3.5ppm from –40 to +85 degrees C. (This later is equivalent to +/- 2 minutes per
year.) The clock counts from seconds to years and includes leap-year compensation to year 2099. There are two alarm
register sets with time and date comparators. Enable registers enable one or both alarm systems to drive the interrupt
JED AVR595 User’s Manual (Dec 2nd 2010 © JED Microprocessors Pty Ltd)
Page 6
output pin. This can be used to either power up a completely powered-down system via power supply control logic, or
generate a PIN-CHANGE interrupt to a power-up CPU which is in idle mode.
The local temperature of the RTC chip can be read out of a register in the RTC. This is effectively the PCB temperature,
as the RTC power dissipation is close to zero. The temperature accuracy is +/- 3 degrees Centigrade. Data is read out as
a 9 bit number plus sign, with 0.25 degrees Centigrade resolution.
The RTC is powered by a 3v lithium rechargeable battery from Panasonic. This allows the RTC to continue operating
when the main board supply is turned off and recharged via an onboard constant current charging circuit when the board
is powered up. (See: http://datasheets.maxim-ic.com/en/ds/DS3232.pdf )
DataFlash 8MByte Flash memory
This chip (AT45DB642D-TU, U9) is accessed via the SPI bus and provides high-speed sector-erased data storage with
sector-sized dual ram buffering on the chip. Port PG5 is the DataFlash chip select (low true). This can be accessed at
high speed as linear memory space for data logging storage, as look-up memory for industrial processes or can even be
formatted as a FAT file system and used for conventional file storage applications, maybe in conjunction with a
SD/MMC memory card, and files transferred by name between storage devices.
It can also hold replacement images of the main CPU Flash memory, loaded via a communications interface, checked,
and then loaded into the CPU via a boot-loader for remote field updates of far-away systems.
(See http://www.atmel.com/products/DataFlash/ for data on the DataFlash devices);
FRAM non-volatile 32Kbyte memory
An FM24C256 or FM24C512, 32/64 Kbyte Ramtron FRAM (Ferroelectric Nonvolatile RAM (see (via I2C), is
provided for data buffering and non-volatile short-term storage during data logging. It has a 10 billion read/write cycle
life (compared with 100,000 operations typical for EEPROM) and does not have the 10 ms erase and write times of an
EEPROM. Typical applications are for full sector buffers for data being assembled prior to writing to DataFlash or USB
memory stick. Data is generated by events as small records, and then written when a full sector has accumulated in the
FRAM. This has speed and power consumption advantages in applications where data is needed in a steady stream, or
needs to be logged with minimum power consumption.
(See: http://www.ramtron.com/lib/literature/datasheets/FM24C256ds_r3.1.pdf ) The FRAM devices are an interesting
technology. (See: http://www.ramtron.com/doc/AboutFRAM/Default.asp );
Eight Analog or Digital Inputs and Delta-Sigma ADC (Schematic sheet 6)
The Atmega2561 provides eight channels of analog input via CPU port PF0 … 7 on J13 and J14. This has 10 bits
conversion resolution, and various in-CPU modes and control register bits combining channels in differential modes,
control speed of the conversion clock, controlling gains on some channels and can even close the CPU down into a
‘quiet’ mode for lower-noise conversions. (Twenty-two pages are devoted to the ADC in the chip manual.)
Inputs
The eight “analog” inputs all can have user-installed pull-down resistors (eg 200 Ohms to terminate 4-20 mA current
sources), can have user-installed pull-up resistors to Vcc to provide a top resistor and hence, current to a resistive
transducer with one end to ground, a user-installed series resistor for protection, and then an optional second pull-down
resistor as the bottom end of the divider pair (working with the series resistor), to scale higher input voltage input ranges
to a range of 0 to 4.096 volts. The analog range is 0 to 4.092 volts for a count of 0-3FFh. The configurations of these
loaded resistors for gain, pull-up or pull-down are shown on sheet 6 of the schematic.
All pins of these “input” pin group can be used for digital inputs (read in parallel as CPU ports PF0 … PF7.)
(Alternatively, FETs can be loaded with Source to socket strip pin 3 (Gnd.), Drain to pin 4 (external screw terminal) and
Gate to pin 5 (CPU) and these can become four groups of four general-purpose outputs. (If FETs are loaded, 4K7
resistors must be loaded between pins 6 and 7 of the strips associated with each line from the FET gates to Gnd.) See
Sheets 3 for a loading diagram. (Not available on prototype as holes are too small).
JED AVR595 User’s Manual (Dec 2nd 2010 © JED Microprocessors Pty Ltd)
Page 7
Delta-Sigma ADC
The AVR595 is also equipped with a 4 input high resolution, 24 bit delta-sigma ADC chip from Linear Tech
(LTC2492) See: http://cds.linear.com/docs/Datasheet/2492fd.pdf
This allows ultra fine resolution via a wide-range filtered micro-volt input signal direct conversion system which is
ideal for thermocouples, etc. ADC filtered power is supplied via LC3 and bypass caps and ultra low leakage protection
diodes are provided across all inputs. J12 provides access to the 4 ADC inputs as well as a filtered 5v output.
Four FET Outputs, 1-Wire and External Interrupts (Schematic sheet 7)
4 high current sinking FET outputs
These are on J9 via PD6-PD7 and PE2-PE3.
Pull up or pull down resistor networks may be installed in L13 on these open drain outputs if desired.
Another 4 FET’s may be added on J8 if required instead of the interrupts on PB5-PB6 and digital inputs on PD4-PD5.
6 External Interrupts and 2 Digital Inputs
These are on CPU pins PE4…PE7, PB5-PB6, PD6-PD7 and are available via J9 and J10 with 4k7 current limit
resistors and 4v7 protection diodes. PE4…PE7, and PB5-PB6 are also “pin change” interrupt inputs which can power
up a sleeping system, and/or generate an interrupt on the rising or falling edge, or a “low” level. The PB5 and PB6 pins
can also be used as output compare match pins for generating an external PWM signal.
1-Wire Interface
This interface uses connector J10.5 via CPU port pin PE7. R28 is installed if this option is desired and a pullup to Vcc
is provided via the resistor network installed in L14.
(If not used as a 1-Wire interface, this pin can be used as a general-purpose I/O pin with pull up.)
CPU FLASH programming/re-programming
The AVR595 is programmed via the RX0, TX0, SCK and RESET* pins, which appear on a 6-pin header (J1)
compatible with the Atmel’s AVRISP MKII. This can program any part of the CPU FLASH memory, including the
boot sectors. These are stocked by JED in Australia, and have a USB connection to the development PC. See:
www.atmel.com/dyn/products/tools_card.asp?family_id=607&family_name=AVR+8%2DBit+RISC+&tool_id=3808
The CPU book block sector can be loaded with a loader program to enable this board’s CPU FLASH to be reloaded
from a section of the DataFlash memory on reboot, and as this memory can be loaded by the CPU over any
communications or file transport system provided on the board, potentially the CPU could be re-programmed from:
•
•
•
A file on a USM memory stick;
A file transferred via any RS232 serial port;
A file transferred via radio/GSM link
In each case, the user CPU program sets up the re-program sequence, communicating with its host or unloading a
transferred file into the allocated DataFlash sectors (and checking it with a CRC checksum). Then CPU sets some flags
in the CPU eeprom, and does a jump to the restart address. On startup in the boot loader, the system checks the eeprom
flags, and if set, proceeds to erase the CPU FLASH memory and re-writes it from the file, again doing a CRC check.
When re-loaded and checked, the CPU clears the eeprom flags, and restarts again, this time (as the flag is NOT set) the
user program starts normally, “phones home” and tells the control centre a successful reload has occurred.
The user-written program would be responsible for transferring the file to the DataFlash nominated area in whatever
way was convenient, but they would all use the same boot loader in the boot sector of the DataFlash, which JED would
provide.
JED AVR595 User’s Manual (Dec 2nd 2010 © JED Microprocessors Pty Ltd)
Page 8
AVR programming languages.
Many different compilers are available for the AVR, and assembly language can even be used, via the free “Studio”
software from Atmel’s web site or supplied with the AVR ISP programmer on CD. Atmel list compiled language
support from 16 different companies at: http://www.atmel.com/products/AVR/thirdparty.asp#compilers
At JED we have used the CodeVison C compiler for many years, and highly recommend it for large-scale projects as a
very good implementation of ANSI C with good embedded libraries and good “code-wizards” for AVR hardware
support (I2C, SPI, 1-Wire, LCD, SD/MMC etc). See: http://www.hpinfotech.ro/
We have also used the BASCOM BASIC compiler from MCS Electronics, and found it a simpler system than the C, but
easily picked up by beginners. It has built-in I2C, SPI, UART, LCD, 1-Wire support, simulator, etc. See
http://www.mcselec.com/index.php?option=com_content&task=view&id=14&Itemid=41
There is also an AVR PASCAL compiler from mikroElectronica ... it seems easy to “pick up” and use. It has SD/MMC
support built in, as well as I2C, SPI, 1-Wire etc. See: http://www.mikroe.com/en/compilers/#avr ),
There is also the free “gnu avr-gcc” tool-set, including the WinAVR IDE. See:
http://www.avrfreaks.net/index.php?module=FreaksTools&func=viewItem&item_id=145
There are also a lot of code support products reviewed at the very popular dedicated AVR sites:
http://www.avrfreaks.net/
http://www.atmel.com/products/avr/thirdparty.asp
A customer support disk is also supplied with the board which contains demo code written in C using the CodeVision C
complier mentioned above. This code shows how to access all CPU functions in addition to things like setting up serial
comms, doing ADC conversions, reading inputs and driving outputs, reading and writing to the dataflash memory and
talking to the VDrive.
JED AVR595 User’s Manual (Dec 2nd 2010 © JED Microprocessors Pty Ltd)
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