Comtech EF Data DD2401 - Manual (Page 38)

User Interfaces DD2401 Satellite Demodulator
4- 14 MN-DD2401 - Rev. G
packet; but with the same . When the intended receiver detects a duplicate packet, the
packet is acknowledged with a response packet and internally discarded to preclude undesired
repetitive executions. If the M&C computer sends a command packet and the corresponding
response packet is lost due to a system or internal error, the computer times out and re-transmits
the same command packet with the same to the same receiver and waits once again for
an acknowledgment or a NAK packet.
To reiterate, the format of the message block is shown in Table B-4, Link Level Protocol Message
Block.
Table 4-6. Link Level Protocol Message Block
SYNC COUNT SOURCE
ADDRESS
DESTINATION
ADDRESS
FSN OPCODE DATA
BYTES
CHECKSUM
The RLLP Remote Port Packet structure is as follows:
Message format header character that defines the beginning of a
message. The character value is always 0x16. (1 byte)
Number of bytes in the field. (2 bytes)
Identifies the address of the equipment from where the message
originated. (1 byte)
Identifies the address of the equipment where the message is to be sent.
(1 byte)
Frame sequence number ensures correct packet acknowledgment and data
transfers. (1 byte)
This byte identifies the message type associated with the information
data. The equipment processes the data according to the value in this field. Return error
codes and acknowledgment are also included in this field. (2 bytes)
<...DATA...> Information data. The number of data bytes in this field is indicated by
the value.
The modulo 256 sum of all preceding message bytes excluding the
character. (1 byte)
4.4.9 DD2401/DD2401L Opcode Command Set
The DD2401/DD2401L Opcode Command Set is listed below, separated by commands that
control the demodulator, or the entire module.
4.4.10 Demodulator Command Set
RLLP Command Opcode
Query Demodulator All 2401h
Query Demod Latched Alarms 2406h
Query Demod Current Alarms 2409h
Query Demod Status 240Ch
Query Demod Eb/No, Input Level, Raw BER, Corrected
BER, and Frequency Offset, AGC Voltage 240Dh
Query Demod Lock Status 2437h