Comtech EF Data SDM-100A - Manual (Page 154)

Remote Control Operation SDM-100A Satellite Modem
A–2 Rev. 0
A.2 Message Structure
The ASCII character format used requires 11 bits/character:
• 1 start bit
• 7 information bits
• 1 parity bit
• 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. 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.