Micro | Digital Satellite Receiver | AN2677/D: Digital Satellite Equipment Control (DiSEqC) using

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Application Note
AN2677/D
3/2004
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Digital Satellite Equipment
Control (DiSEqC ) using
MC68HC908QT/QY
By Stanislav Arendarik
Motorola Czech System Application Laboratory
Roznov pod Radhostem, Czech Republic
Introduction
This document describes using the Motorola MC68HC908QT/QY series
microcontroller unit (MCU) as the DiSEqC  (digital satellite equipment control)
slave. The in this application note is a twin satellite/LNB switch, but it could
easily be adapted to other applications, such as a dual LNB (twin LNB
integrated within same horn), or a four satellite/LBN switch (or quad LNB). With
appropriate hardware and software enhancements, many other features can
be implemented.
The DiSEqC system is divided to two main groups: level 1.x and level 2.x.
•
•
Level 1.x — One-way communication between integrated receiver
decoder (IRD) and satellite outdoor unit (ODU).
Level 2.x — Two-way communication that supports a return-signalling
path and multiple peripheral devices.
The DiSEqC system uses the existing coaxial cable as the communication bus
that connects satellite receivers and satellite peripheral equipment. DiSEqC
control is a standard solution that replaces other analog control systems and
wiring.
According to the DiSEqC bus specification, the advantages of DiSEqC are:
•
•
•
•
•
•
Standardized digital system with non-proprietary commands
Enables switching in multi-satellite installations
Backwards compatible with 13/18 volt and 22-kHz tone switching
Potential for reduced power dissipation and thus cost reduction and
improved reliability
No switching problems caused by incompatibility of system components
Simplified receiver installation using device recognition via optional
two-way communication
DiSEqC is a trademark of Eutelsat.
ncorporates SuperFlash technology licensed from SST.
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AN2677/D
DiSEqC Introduction
The DiSEqC standard is a single master, single or multiple slave system, so
communications may be initiated only by the master tuner-receiver/IRD. The
The slave devices can be switches, LNBs (low noise blocks), positioners, or
other special devices used to establish satellite program reception.
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The bus transfers:
–
–
–
–
dc power supply — usually 13-V/18-V; max 500 mA
RF signal — IF band from 950 MHz to 2150 MHz
22-kHz tone signal — nominal 650 mV (± 250 mV) peak-to-peak
DiSEqC data modulated on the 22-kHz tone signal (if used)
To help ensure the transport of the 22-kHz signal, the total load capacitance of
the entire bus (cable) should not exceed 250 nF. At this load, the bus can
tolerate a cable as long as 50 meters. DiSEqC peripherals should not load the
bus by typically more than 100 nF. For certain classes of devices such as
SMATV (satellite master antenna television) nodes and installer aids, a much
lower value is preferred.
DiSEqC
Signal/Protocol
See the DiSEqC bus specification from http://www.eutelsat.com for complete
bus specification.
There are several signal possibilities on the bus:
•
Earlier non-DiSEqC units (one-band LNBs)
– dc current of 13-V/18-V (for switching horizontal/vertical (H/V)
polarization)
•
Earlier non-DiSEqC units (two-band LNBs)
– dc current of 13-V/18-V (for switching between H/V polarizations)
– Continuous 22-kHz tone signal for low or high band selection
•
Non-DiSEqC messages
– dc current of 13-V/18-V (for switching between H/V polarizations)
– Continuous 22-kHz tone signal for low or high band selection
– Tone burst signalling to switch between A and B positions of
two-band LNBs
•
Any combination of these signals and DiSEqC messages
It is possible to have DiSEqC and non-DiSEqC signalling on the bus. Having
both types of signals on the bus allows the user to control accessories of both
types and does not require the user to configure the master tuner-receiver/IRD
to a particular command protocol. This is possible because the control data of
both protocols should be the same, and a DiSEqC slave (MC68HC908QT/QY)
will recognize and perform control signals from both command protocols.
2
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DiSEqC Introduction
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Application
Characteristics
This application using the MC68HC908QT4 as the DiSEqC slave has the
following characteristics:
•
Two LNBs will be controlled (default is satellite A).
•
Because the MC68HC908QT/QY series is compatible with non-DiSEqC
control, it is possible to use the earlier satellite receivers with voltage
(13 V to 18 V), tone (22 kHz present or not), and tone-burst control
capabilities.
•
The switch (MC68HC908QT4 plus additional components)
automatically detects whether the tone-burst protocol or DiSEqC is
used. After power-up or reset, the ODU can recognize tone-burst or
DiSEqC control; after DiSEqC control is received, tone-burst control is
blocked.
•
DiSEqC level 1.0 will be used.
•
The following bus commands are recognized by the DiSEqC slave:
– Framing byte:
$E0, $E1
– Address byte:
$00 — Any device (master to all devices)
$10 — Any LNB, switcher or SMATV
– Command byte:
$00 — Reset DiSEqC microcontroller (MC68HC908QT/QY)
$02 — Switch peripheral power supply OFF
$03 — Switch peripheral power supply ON
$22 — Select satellite position A
$23 — Select switch option A (e.g., position A/B)
$26 — Select satellite position B
$27 — Select switch option B (e.g., position C/D)
$38 — Write to port group 0
– Port group 0 data (first data byte):
$F8, ($FA, $FC, $FE) — Switch to satellite A
$F0, ($F2, $F4, $F6) — Switch to satellite B
Because this application uses level 1.0, basic DiSEqC bus commands and the
low pin count MC68HC908QT4 are used. Other commands may be added for
possible new functions. The MC68HC908QT4 can control a maximum of four
LNB for DiSEqC level 1.0 commands. In this case, only two outputs are used,
and two are left free. It is possible to implement this software for MCU
MC68HC908QY4 to obtain a higher pin count and more control capability to
satisfy the DiSEqC level 1.1 or level 1.2 requirements.
The MCU uses the FLASH programmed value for the TRIM register. This value
ensures good accuracy of the bus frequency.
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Figure 1 shows the signal block diagram. There are two universal LNBs used,
receiving signals from satellite A and B respectively. The ODU
(MC68HC908QT4 and some other components) receives the command data
signal from the IDU. The commands are sent in the DiSEqC data format
(modulated 22 kHz) through the high frequency coaxial cable.
UNIVERSAL LNB
UNIVERSAL LNB
SAT A
SAT B
MC68HC908QT4
DiSEqC LEVEL 1.0
ODU
HF SIGNAL
TO IDU
COAX CABLE:
dc SUPPLY
22 kHz
COMMANDS FROM IDU
Figure 1. Signal Block Diagram
Figure 2 shows the functional block diagram. The satellite receiver is
connected by the coaxial cable to the pin called “IF-Out” (4).
This cable carries:
•
Supply voltage +13 V or +18 V at 0.5 A max from the satellite receiver
to the LNB switch and the target LNB (LNB-A or LNB-B)
•
DiSEqC or non-DiSEqC commands from the satellite receiver to the
LNB switch and the target LNB
•
High-frequency television signal in the IF band (950 MHz to 2150 MHz)
from that LNB through the LNB switch to the satellite receiver
The universal LNBs are controlled by:
4
•
Supply voltages
– +13 V — vertical polarization
– +18 V — horizontal polarization
•
22-kHz signal superimposed on those voltages
– 22-kHz signal is present — high band (11.7 GHz to 12.75 GHz) is
received
– 22-kHz signal is not present — low band (10.7 GHz to 11.7 GHz) is
received
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AN2677/D
DiSEqC Introduction
ODU
(1)
SWITCH
SAT A
IF OUT
(4)
COAX. CABLE
SAT B
22-kHz
NETWORK
(1)
(3)
(2)
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CONTROL CIRCUIT
WITH MC68HC908QTY MCU
NOTES:
1. I/O FROM SATELLITE LNB (IF 950 MHz TO 2150 MHz, dc SUPPLY, 22 kHz SIGNAL)
2. MODULATED DiSEqC DATA
3. CONTROL SIGNALS FROM MCU
4. COAX. CABLE BETWEEN ODU AND RECEIVER
(dc SUPPLY 20 V, DiSEqC DATA, IF BAND TO RECEIVER)
Figure 2. Functional Block Diagram
The MC68HC908QT4 MCU receives the DiSEqC control message, decodes it,
and controls the RF PIN-diode switch.
The DiSEqC switch unit (DSU) controlled by the MC68HC908QT4 MCU allows
both DiSEqC and non-DiSEqC control signals from the satellite receiver to be
used.
The satellite receiver sends the control message to the LNB switch in
accordance to DiSEqC standard level 1.0 (see References). The LNB switch
switches between LNB-A or LNB-B. The supply voltages and the 22-kHz signal
are produced by the IDU (satellite receiver). The capabilities of this control unit
with the MC68HC908QT4 can be expanded to a maximum of four LNBs
(LNB-A, -B, -C, and -D) in accordance with DiSEqC level 1.0 control standard.
DiSEqC Slave
Modes
The DSU (DiSEqC switch unit) works in two main modes, based on the type of
control:
–
–
Non-DiSEqC Control
(VFC Mode)
Non DiSEqC control — voltage/frequency/burst control (VFC)
DiSEqC control
In VFC mode, the DSU is not sensitive to voltage changes (+13 V or +18 V) or
the presence of the 22-kHz signal.
The signal (voltage and 22-kHz tone) is generated by the satellite receiver to
switch the target LNB between H/V polarizations, and between the low and high
bands received (22 kHz absent/present). The DSU is through-hold for this
signal.
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AN2677/D
The DSU in VFC mode is sensitive to tone burst signaling. This control signal
enables switching between LNB-A and LNB-B, respectively. This is described
in the DiSEqC bus specification from Eutelsat (see References).
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DiSEqC Control
If the DSU receives a DiSEqC message from the IDU, it decodes it and
switches between satellite A or satellite B inputs according to the received
control command.
Table 1 summarizes all states that can be used within this small DSU. It’s
possible to receive all programs from two different satellites in the horizontal
and vertical polarization, both in the low and high bands. The detailed
description of the message format is in the DiSEqC bus specification from
Eutelsat (see References).
Table 1. States of DiSEqC Slave Unit
DiSEqC Slave Unit
Description
State
LNB
A/B
Polar
H/V
Band
L/H
1
A
V
L
2
A
V
H
3
A
H
L
4
A
H
H
5
B
V
L
6
B
V
H
7
B
H
L
8
B
H
H
Msg 1
$E0 $10 $22 ($23, $03, $00)
or $E0 $10 $38 $F8
$E0 $10 $26 or $E0 $10 $27
or $E0 $10 $38 $F4
The schematic is shown in Figure 3.
The MC68HC908QT4 MCU is powered by the supply net, which comprises L3,
C6, R6, D4, C4, and C5. The supply voltage ranges from 4.5 Vdc to 5.0 Vdc,
depending on the kind of zener-diode.
The MCU receives control messages through pin 5 (IRQ). The 22-kHz net
comprises L3, C6, R6, C7, R8, and the Q3 circuit.
The outputs from the MCU are pins 2 and 3. These outputs control the two dc
switches according to the control messages received. The first dc switch
comprises Q1, Q2, D1, D2, and associated components. The second dc switch
comprises Q4, Q5, D3, D6, and associated components. The desired LNB is
powered from the IDU through the Q1 (Q5 opposite channel) and low-pass filter
L1, C1, and L2 (L5, C8, and L4 opposite channel). The IDU (satellite receiver)
produces the desired power supply, +13 V or +18 V respectively, and
superimposes the 22-kHz signal if needed.
6
Digital Satellite Equipment Control (DiSEqC) using MC68HC908QT/QY
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DiSEqC Introduction
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The high-frequency circuit comprises D1, D2, and C3 (D6, D3, and C3 opposite
channel). Resistor R5 is used to switch the desired PIN-diode pair when the
supply voltage is present on the same LNB port. The opposite PIN-diode pair
is switched off by the reverse voltage. It is very important to design the correct
shape of the high-frequency circuit to match the impedance of the LNB to the
coaxial cable (both are 75 Ω).
The output pin 4 (PTA3) is used to send a message back to the IDU by two-way
communication (in levels higher than level 1.0). It’s possible to use a simple
circuit (transistor Q6 with associated components) to produce a pseudo
square-wave 22-kHz signal. This signal doesn’t comprise the high-frequency
disruptive components because of the value of the resistor R7 and the relatively
high capacitance of the coaxial cable line (about 50 nF to 100 nF). The two-way
communication option is not used in this design example.
The complete DiSEqC slave unit is packaged in a metal case with three
F-terminals, which is standard in satellite devices. The PCB is double-sided
with a bottom ground plane. The top side of the PCB is shown in Figure 4, and
the complete encased DiSEqC slave unit in Figure 5.
Digital Satellite Equipment Control (DiSEqC) using MC68HC908QT/QY
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LNB-A
REC
LNB-B
47nH
100p
L4
D6
D3
D2
L2
D1
C8
100p
C3
330p
C6
L3
100p
C1
47nH
BAR89
BAR89
BAR89
BAR89
47nH
MOTOROLA
47nH
L5
2k2
R5
47nH
Q5
Q1
10k
330p
C9

Digital Satellite Equipment Control (DiSEqC ) using MC68HC908QT/QY
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Q4
560R
R10
D4
560R
R2
Q2
+
Q6
22n
C7
C4
10uF
18R
R11
1k
R8
100n
C5
D5
22k
R4
Q3
Date:
Size
A
Title
2k2
R3
1
2
3
4
U1
Vss
PTA0
PTA1
IRQ
33k
R13
Monday, December 01, 2003
Document Number
RTAC TC105 00186.00
47k
R14
MC68HC908QT4
Vdd
PTA5
PTA4
PTA3
DiSEqC Slave QT4 - V2.0
4k7
R12
Q7
8
7
6
5
Sheet
1
of
1
PBSS5350T
Q1, Q5
BC847C
Type
Reference
Q2, Q3, Q4, Q6, Q7
Figure 3. DiSEqC Slave Schematic
270R
R7
R9
1k
R6
10k
R1
330p
C2
BZV55C4,7
L1
1N4148
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Rev
00
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AN2677/D
DiSEqC Introduction
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AN2677/D
DiSEqC Introduction
Figure 4. DiSEqC Slave PCB
Figure 5. DiSEqC Slave Unit — Ready to Use (46 x 30 mm)
Digital Satellite Equipment Control (DiSEqC) using MC68HC908QT/QY
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AN2677/D
Software Operation
START
BASIC INITIALIZATION
SAT A AS DEFAULT
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ENABLE TONE-BURST
ENALBE DiSEqC
NO
RECEIVED VALID DATA
?
YES
YES
DECODE, ANSWER,
AND SET OUTPUTS
RECEIVED TONE-BURST DATA
?
NO
RECEIVED DiSEqC DATA
?
NO
YES
YES
RESET COMMAND RECEIVED
?
NO
DECODE, ANSWER, AND
SET OUTPUTS
DISABLE
TONE BURST
Figure 6. Software Operation
10
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AN2677/D
Conclusion
Conclusion
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This application note explains the DiSEqC-control of low noise blocks in a
satellite receiver system and demonstrates the basic possibilities of a DiSEqC
slave unit. To achieve the basic properties of DiSEqC level 1.0, a member of
the low-cost and powerful small (8-pin) universal MCU MC68HC908QT4 series
can be used. In this case, pins 6 and 7 are available to be used in the function
control ports for the next two LNBs. To satisfy the demands of DiSEqC level 1.x
and 2.x, it’s possible to use a similar MCU from the higher pin count
MC68HC908QY4 series.
References
AN2677SW.zip — from Motorola (http://motorola.com/semiconductors);
contains all software files and schematic for this application.
DiSEqC Bus Functional Specification V4.2 — from Eutelsat
(http://www.eutelsat.com)
MC68HC908QY4/D: MC68HC908QT4 Data Sheet — from Motorola
(http://motorola.com/semiconductors)
NOTE:
With the exception of mask set errata documents, if any other Motorola
document contains information that conflicts with the information in the device
data sheet, the data sheet should be considered to have the most current and
correct data.
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