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XE2420

The World’s First Complete PLCC Packaged Modem

Unspecified 

XE2420 AT Commands

The XE2420 uses "AT" commands for configuration and

control. This section describes use of the AT command

format and lists the AT commands, Registers and Result

codes. XE2420 "AT" commands have two operational

modes; Command Mode and Data Mode.

Command Buffer - No more than 36 characters,

including the AT prefix, may be loaded into the com-

mand buffer. If the command buffer overflows, the

modem issues an "ERROR" result code and commands

are not executed.

Data Mode: The XE2420 enters data mode after it

connects with a remote modem and issues the appropri-

ate result code. In the Data Mode the modem sends all

data presented on Transmit Data (/TXD) to the remote

modem and puts data from the remote modem onto

Received Data (/RXD). When the modem exits data

mode, it issues a "NO CARRIER" result code.

Command Mode: The XE2420 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 - Each command, except the A/

command, begins with the AT prefix. The "A" and "T"

may be either both upper case or both lower case but

cannot be of different cases. The prefix identifies the

speed and parity of the commands sent to the modem by

the host. Speed is determined by measuring the width of

the incoming bits. Parity is determined by comparing the

parity bit of the "A" and the "T."

Command Line - Commands may be strung together in

a single command line of up to 36 characters. Com-

mands are executed in the sequence they appear. Spaces

may be inserted into the command line but do not fill

space in the command buffer. A carriage return termi-

nates 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 Line Editing - The backspace edits a

command line before it is executed. 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 back-

space to edit the command line.

Re-Execute Last Command - The A/ command causes

the modem to re-execute the last command line. This is

the only command which does not require the "AT"

prefix.

Omitted Parameters - Most commands include a pa-

rameter which determines how the functions will be set.

When the command parameter is omitted from the

command string, it is assumed to be a 0.

Escape Characters - A 3 character escape sequence

maybe entered while in data mode to switch the modem

into command mode while on line. The escape charac-

ter, 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,

one or two digit 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

(7)

XE2420

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