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CDM-600L Satellite Modem
BUC FSK Communications
On power-up, the Tx carrier is Off until the BUC is commanded to turn the carrier
on (unless the unit is commanded into the power On mode at the factory). The
BUC does not allow the carrier to be turned On unless the PLL is locked, and
automatically turns the carrier Off in the event the PLL goes out-of-lock. If the
PLL then comes back into lock, the BUC restores the carrier to the most recent
requested state by the IDU. The carrier enable/disable function is implemented by
switching On/Off the switched regulators of the BUC amplifier chains (a "sleep
mode").
The BUC is equipped with a calibrated power sensor for measuring the power
delivered to the antenna for rated output to 20 dB backed off. This value, in dBm,
is available via the M&C for power level monitoring and AGC.
Refer to BUC manufacturer specifications for reported power accuracy.
17.1.1
Transmission Interface
Each transmitted data packet consists of 7 bytes of information. The BUC only
accepts a command if the first data byte contains the appropriate address.
Commands are only executed if the checksum coincides, but a status response is
sent if the address is correct and the command number is within the valid range.
17.2
Message Structure
17.2.1
Command Message Structure (CDM-600L to BUC)
Byte
1
2
3
4
5
6
7
Name
Address
Address of BUC
Command
Request Status
Tx On/Off
Change Address
Set Carrier Frequency
Data Byte 1
Not used if command:
Tx control if command:
New address if command:
Carrier Frequency if command:
Data Byte 2
Not used if command:
Not used if command:
Not used if command:
Carrier Frequency if command:
Data Byte 3
Not Used
Data Byte 4
Not Used
Checksum
Algebraic sum of bytes 1 - 6
17–2
Description
= 0x01
= 0x02
= 0x03
= 0x04
= 0x01
= 0x02
= 0x03
= 0x04
Revision 2
MN/CDM600L.IOM
Value
0x01 to 0x0f
0x01
0x02
0x03
0x04
0xAA
0=Off, 1=On
0x01 to 0x0f
MSbyte
0XAA
0xAA
0xAA
LSbyte
0xAA
0xAA
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