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Message structure, Start character, Device address – Comtech EF Data SNM-1002 User Manual

Page 128

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SNM-1002 LinkSync

 Modem

Revision 2

Remote Control Operation

MN/SNM1002.OM

A–2

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.