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B.2 message structure, B.2.1 start character, B.2.2 device address – Comtech EF Data SDM-9000 User Manual

Page 220

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Remote Control Operation

SDM-9000 Satellite Modem

B–2

Rev. 4

B.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

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:

“<”

for commands

“>”

for responses

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. 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.