Comtech EF Data SNM-1001L - Manual (Page 224)

SNM-1001L Satellite Modem Revision 1
BUC FSK Communications MN/SNM1001L.IOM
13–2
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.
13.1.1 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.
13.2 Message Structure
13.2.1 Command Message Structure (IDU to ODU)
Byte Name Description Value
1 Address Address of BUC 0x01 to 0x0f
2 Command Request Status
TX On/Off
Change Address
Set Carrier Frequency
0x01
0x02
0x03
0x04
3 Data Byte 1 Not used if command: = 0x01
TX control if command: = 0x02
New address if command: = 0x03
Carrier Frequency if command: = 0x04
0xAA
0=Off, 1=On
0x01 to 0x0f
MSbyte
4 Data Byte 2 Not used if command: = 0x01
Not used if command: = 0x02
Not used if command: = 0x03
Carrier Frequency if command: = 0x04
0XAA
0xAA
0xAA
LSbyte
5 Data Byte 3 Not Used 0xAA
6 Data Byte 4 Not Used 0xAA
7 Checksum Algebraic sum of bytes 1 - 6