Message Structure; Start Character; Device Address; B.2 Message Structure - Comtech EF Data SDM-300A Installation And Operation Manual

Remote Control Operation
B.2

Message Structure

The ASCII character format used requires 11 bits/character:
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Messages on the remote link fall into the categories of commands and responses.
Commands are messages which are transmitted to a satellite modem, while responses are
messages returned by a satellite modem in response to a command.
The general message structure is as follows:
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B.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:
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B.2.2

Device Address

The device address is the address of the one satellite modem which is designated to receive
a transmitted command, or which is responding to a command.
Valid device addresses are 1 to 3 characters long, and in the range of 1 to 255.
Note: Address 0 is reserved as a global address which simultaneously addresses all devices
on a given communications link. Devices do not acknowledge global commands.
Each satellite modem which is connected to a common remote communications link must
be assigned its own unique address. Addresses are software selectable at the modem, and
must be in the range of 1 to 255.
B–2
1 start bit
Information and Parity bits (select one)
! 7 information bits and 1 parity bit (Odd/Even)
! 8 information bits (None)
2 stop bits
Start Character
Device Address
Command/Response
End of Message Character
"<"
for commands
">"
for responses
SDM-300A Satellite Modem
Rev. 4