Info 7

The AT Command List

How often have you needed to check an AT command but couldn't find the user manual for your modem?

If it's as often as I do, then you need our list of AT commands.

+++

Keying [shift] and +++ simultaneously causes most modems to revert from the on-line mode to the command mode

, in order that you can issue AT commands to your modem.

Please note that some modem manufacturers objected to paying a royalty to use this command and implemented their own version.

A

Answer Command

Command Syntax - ATA

The A following AT instructs the modem to go off-hook (on-line).

A/

Re-issue Previous Command Line

Command Syntax - A/

The A/ command does not require an Enter keypress.

NOTE: This command is not supported by all modems.

B

Select Communication Protocol

Command Syntax - ATBX

Where:

B0 = ITU-T V.22 at 1200bps

B1 = Bell Standard 212A at 1200bps

In the instance shown here, the BX is used to provide compatibility between 1200bps protocols which are operationally incompatible.

Some modems use the BX command to lock the communication protocol into a user selected setting from the range of protocols provided by the modem.

D

Dial and Dial Modification Commands

Command Syntax - ATDXYZAABBCC

Where:

D is the dial instruction, which is then followed by the number to be dialled and modifier characters which affect the dialling procedure.

0 thru' 9 and */# = dialled numbers and symbols
A to D = Special MF codes supported by some modems
T = Instruction for modem to dial using Tone signalling
P = Instruction for modem to dial using pulse (aka loop-disconnect) signalling
, (comma) = Instruction for modem to pause before continuing the dial command string
This command can be used more than once in a dial command string ie ATDP9,,01225864600.

Note, however that type approval authorities (BABT, DGPT etc) have rules concerning the length of time a modem can pause while dialling, so don't add more comma's than necessary.
L = Used as ATDL to instruct the modem to re-dial last number
W = Instruction for modem to wait for dial tone before continuing the dial command string. This is a nice command if you are using an American modem (in America), but because manufacturers don't often tweak the secondary dial tone detector in order to detect European dial tones, this feature can operate in a hit-or-miss fashion. Most often, it's quicker to use a comma or two in your dial string to overcome the delay while a PBX returns the PSTN dial tone.

$ = Instruction for modem to wait for bong tone (used to initiate calling card number entry)before continuing the dial command string
! = Instruction (called hookflash in the US) for the PBX to allow the transfer of a call to another extenion
In Europe, the term hookflash is replaced by the term Timed Break Recall which has the same effect.
R = Instruction for the modem to initiate the call in a manner suitable to communicate with modems which can only originate calls
; = Instruction for the modem to return to the command mode after dialling, ensuring that the call connection is maintained
S=n where n = 0 to 3 = Instruction for the modem to dial a stored number

E

Echo Command

Command Syntax - ATEX

Where:

E0 = Don't echo typed characters on the display

E1 = Echo typed characters to the display

H

Hook Switch Control Command

Command Syntax - ATHX

Where:

H0 = Instruction for the modem to resume the on-hook state and await commands

H1 = Instruction for the modem to assume the off-hook condition

Note: Certain type approval authorities forbid the use of this command.

I

Identification Request Command

Command Syntax - ATIX

Where:

I0 = Instruction for the modem to return the modem speed (protocol) setting

I1 = Instruction for the modem to return it's internal ROM checksum value

I2 = Instruction for the modem to return the OK response

I3 = Instruction for the modem to return it's numeric product ID and Firmware checksum value

I4 = Instruction for the modem to return it's bitmap of the modem's features

L

Speaker Volume Command

Command Syntax - ATLX

Where:

L0 = Instruction for the modem to set it's internal speaker to the lowest volume setting

L1 = Instruction for the modem to set it's internal speaker to the low volume setting

L2 = Instruction for the modem to set it's internal speaker to the medium volume setting

L3 = Instruction for the modem to set it's internal speaker to the highest volume setting

M

Speaker Control Command

Command Syntax - ATMX

Where:

M0 = Instruction for the modem to set it's internal speaker to the off setting

M1 = Instruction for the modem to set it's internal speaker to the on setting until carrier signal has been detected

M2 = Instruction for the modem to set it's internal speaker to the on setting

M3 = Instruction for the modem to set it's internal speaker to the on setting until carrier signal has been detected, except while dialling.

N

Modulation Fallback Command

Command Syntax - ATNX

Where:

N0 = Instruction for the modem to handshake only at the speed set in S-Register 37 (regardless of whether the call is being originated or answered)

N1 = Instruction for the modem to originate and answer calls at the highest DCE speed set in S-Register 37, but fall back to a slower speed if necessary

O

Return to On-line Mode Command

Command Syntax - ATOX

Where:

O0 = Instruction for the modem to assume the off-hook state

O1 = Instruction for the modem to assume the off-hook state and start the equalizer retraining sequence

Q

Enable/Disable Result Code Command

Command Syntax - ATQX

Where:

Q0 = Instruction for the modem to display result codes

Q1 = Instruction for the modem not to display result codes

SR?

Command to Display S-Register Setting

Command Syntax - ATSR?

Where:

? = Number of the S-Register to be interrogated

SR=

Command to Display S-Register Setting

Command Syntax - ATSR=X

Where:

X = Value to be written to the S-Register specified in SR

V

Select Result Code Format Command

Command Syntax - ATVX

Where:

V0 = Instruction for the modem to display result codes as numbers

V1 = Instruction for the modem to display result codes as words

W

Call Negotiation Progress Command

Command Syntax - ATWX

Where:

W0 = Instruction for the modem not to display negotiation progress

W1 = Instruction for the modem to display negotiation progress

W2 = Instruction for the modem not to display negotiation progress, but to display CONNECT messages instead

X

Extended Result Code Command

Command Syntax - ATXX

Where:

X0 = Instruction for the modem to display the CONNECT, NO CARRIER and RING code messages

X1 = Instruction for the modem to display result codes and connection speed information

X2 = Instruction for the modem to display result codes, connection speed and the DIALTONE code message

X3 = Instruction for the modem to display result codes, connection speed and the BUSY code message

X4 = Instruction for the modem to display result codes, connection speed, BUSY and DIALTONE code messages

Note: The ATX0 command can be used to disable dial tone detection ie force the modem to blind dial, while the ATX4 command instructs the modem to dial only when valid dial tone has been detected.

Z

Modem Reset Command

Command Syntax - ATZX

Where:

Z0 = Instruction for the modem to reset and reload stored user profile 0

Z1 = Instruction for the modem to reset and reload stored user profile 1

UPDATE!

How often have you tried to establish a data or facsimile call to Asia, only to find that your modem times out the call before the called party answers?

Well, its due to the way your call is being routed, and this sequence can easily exceed the 60 seconds limit set by most modem firmware.

This limit is set for good network management reasons and should not be adjusted for reasons other than described above.

If you are experiencing this difficulty, try setting ATS9 to a value of 90 (ATS9=90) and then re-dial.

Remember to set ATS9 back to a maximum value of 60 after the call has been made or you run the risk of ringing you next caller for way too long!

© EPL Ltd, 1995-1997. This document may be reproduced in whole or in part provided that this copyright notice is reproduced on each copy made.

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