Comtech EF Data SDM-300L3 - Manual (Page 354)

SDM-300L3 Satellite Modem Revision 1
Remote Control Operation MN/SDM300L3.IOM
A–2
A.2 Message Structure
The ASCII character format used requires 11 bits/character:
• 1 start bit
• Information and Parity bits (select one)
• 7 information bits and 1 parity bit (Odd/Even) or 8 information bits (None)
• 2 stop bits
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:
• 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
A.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.