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XE1276A

Compact 1200 bps Modem

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AT Commands

The XE1276A uses "AT" commands for modem config-

uration. This section describes the command format

and lists the commands, registers and result codes.

Modes of Operation

The "AT" commands have two operational modes;

Command Mode and Data Mode.

Data Mode: The XE1276A enters data mode upon

connecting with a remote modem and issues an

appropriate "CONNECT" result code. In Data Mode the

modem sends all data presented on Transmit Data

(TXD) to the remote modem and places demodulated

data from the remote modem onto Received Data

(RXD). When the modem exits data mode, it issues the

"NO CARRIER" result code.

Command Mode: The XE1276A enters command

mode on power-up, reset, a lost connection, or receipt

of the escape code. In command mode the modem

accepts commands from the host on transmit data.

Appropriate result codes are returned on received data.

Command Line Format

Command lines issued to the modem follow a strict

format. Each command begins with the prefix AT. The

command line is stored in the command buffer and

executed upon receipt of a carriage return. Until

executed, the command line can be edited with the

backspace key.

Command Prefix - Commands, except A/, begin with

the AT prefix. The "A" and "T" may be both upper case

or both lower case but cannot be of different cases. The

prefix identifies the speed and parity of the commands

sent by the host. Speed is determined by measuring the

width of the incoming bits. Parity is determined by

comparing the parity bits of the "A" and "T."

Command Line - Commands may be strung together

in a single command line of up to 40 characters.

Commands are executed in the sequence they appear.

A carriage return terminates the command line and

causes the commands to be executed. Register S3

allows the user to select a character other than a

carriage return to terminate the command line.

Command Buffer - The command buffer stores up to

40 characters, including the AT prefix, from one

command line. Spaces may be inserted into the

command line without filling space in the command

buffer. If the command buffer overflows, the modem

issues an "ERROR" result code and commands are not

executed.

Command Line Editing - A backspace can be used to

edit a command line before execution. The backspace

key, (Control and H simultaneously on some systems),

erases the previous character in the command line.

Register S5 allows the user to select a character other

than a backspace as the command line editor.

Re-Execute Last Command - The A/ command

causes the modem to reexecute the last command line.

This command does not require the "AT" prefix.

Omitted Parameters - Most commands include a

parameter which determine the function setting. When

the command parameter is omitted from the command

string, it is assumed to be a 0.

Escape Characters - An escape sequence may be

entered while in data mode to switch the modem into

command mode while on line. The escape character,

set by Register S2, must be entered 3 times in

succession within a 1 second guard time to execute the

escape. The default escape sequence is "+++."

Result Codes - The modem issues a result code after

each action. Result codes may be provided as full

words, numeric codes or may be disabled all together.

Each result code ends with a carriage return when

numeric result codes are chosen. When full word result

codes are chosen, a Line feed and Carriage Return

preceed and follow each result code.

XECOM

(4)

XE1276A

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