Comtech EF Data RCS11 - Manual (Page 98)

RCS11 1:1 Redundancy Switch RCS11 Remote Communications
MN-RCS11 – Revision 9 B–4
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 the transmit power
level of a DMD15 modulator), the FSN is incremented after each message packet. When the
FSN value reaches 255, it overflows and begins again at zero. The FSN tag is a powerful tool
that assures sequential information framing, and is especially useful where commands require
more than one message packet.
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 <OPCODE> field of the message
packet from the equipment under control.
If a command packet is sent and not received at its intended destination, a timeout condition can
occur because a response message is not received by the packet originator. On receiving
devices slaved to an M & C computer, the timeout delay parameters may be programmed into the
equipment in accordance with site requirements by Radyne Corp. prior to shipment, or altered by
qualified personnel. The FSN handshake routines must account for timeout delays and be able
to introduce them as well.
B.1.4 Global Response Operational Codes
In acknowledgment (response) packets, the operational code <OPCODE> 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 <SOURCE
ID> with the <DESTINATION ID>, sets the <OPCODE> 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):
RESPONSE OPCODE DESCRIPTION OPCODE
Good Message 000
Bad Parameter 255
Bad Opcode 254
Bad Checksum 253
Command Not Allowed in LOCAL Mode 252
Command Not Allowed in AUTO Mode 251
Bad Destination 250
Unable to Process Command 249
Packet Too Long 248
Table 2. Response OPCODES