Comtech EF Data SMS-301 - Manual (Page 84)

Remote Control Operation SMS-301 Redundancy Switch
A-2 Rev. 3
A.2 Message Structure
The ASCII character format used requires 11 bits/character:
•
7 information bits
•
2 stop bits
•
1 parity bit (Odd/Even)
•
1 start bit
Messages on the remote link fall into the categories of commands and responses.
Commands are messages which are transmitted to a switch, while responses are
messages returned by a switch in response to a command.
The general message structure is as follows:
• Start Character
• Device Address
• Command/Response
• End of Message Character
A.2.1 Start Character
A single character precedes all messages transmitted on the remote link. This character
flags the start of a message. This character is:
•
“<” for commands
•
“
>” for responses
For any command that the 1:1 switch is passing through, an additional start character is
added to the beginning of the message. This informs the operator that this command was
a relayed command. This is true for the modem control link and the operator’s
communications link. In order for a command to be relayed through the 1:1 switch, the
address in the message must match the address that has been assigned to Modem A or
Modem B.