Comtech EF Data SFC1800A - Manual (Page 47)

SFC1800A Synthesized Frequency Upconverter User Interfaces
TM111 – Rev. 1.0 4-23
The Frame Sequence Number (FSN) is included in every message packet, and increments
sequentially. When the M & C computer or bus-linked equipment initiates a message, it assigns
the FSN as a tag for error control and handshaking. A different FSN is produced for each new
message from the FSN originator to a specific device on the control bus. If a command packet is
sent and not received at its intended destination, then an appropriate response message is not
received by the packet originator. The original command packet is then re-transmitted with the
same FSN. If the repeated message is received correctly at this point, it is considered a new
message and is executed and acknowledged as such.
If the command packet is received at its intended destination but the response message
(acknowledgment) is lost, then the message originator (usually the M&C computer) re-transmits
the original command packet with the same FSN. The destination device detects the same FSN
and recognizes that the message is a duplicate, so the associated commands within the packet
are not executed a second time. However, the response packet is again sent back to the source
as an acknowledgment in order to preclude undesired multiple executions of the same command.
To reiterate, valid equipment responses to a message require the FSN tag in the command
packet. This serves as part of the handshake/acknowledge routine. If a valid response message
is absent, then the command is re-transmitted with the same FSN. For a repeat of the same
command involving iterative processes (such as increasing or decreasing transmit power level),
the FSN is incremented after each message packet. When the FSN value reaches 255, it
overflows and begins again at zero.
The full handshake/acknowledgment involves a reversal of source and destination ID codes in the
next message frame, followed by a response code in the field of the message
packet from the equipment under control.
4.4.2.4 Global Response Operational Codes
In acknowledgment response packets, the operational code field of the message
packet is set to 0 by the receiving devices when the message intended for the device is evaluated
as valid. The device that receives the valid message then exchanges the with the
, sets the to zero in order to indicate that a good message was
received, and returns the packet to the originator. This "GOOD MESSAGE" Opcode is one of
nine global responses. Global response Opcodes are common responses, issued to the M&C
computer or to another device, that can originate from and are interpreted by all Radyne
equipment in the same manner. These are summarized as follows all Opcode values are
expressed in decimal form:
Table 4-5. Response OPCODES
RESPONSE OPCODE DESCRIPTION OPCODE
Good Message 000d = 0000h
Bad Parameter 255d = 00FFh
Bad Opcode 254d = 00FEh
Bad Checksum 253d = 00FDh
Command Not Allowed in LOCAL Mode 252d = 00FCh
Command Not Allowed in AUTO Mode 251d = 00FBh
Bad Destination 250d = 00FAh
Unable to Process Command 249d = 00F9h
Packet Too Long 248d = 00F8h