AT Commands

Floyd Kling 

 

AT Command Quick Look-up (common defaults in bold)
Cmd  Function	Cmd  Function	Cmd  Function
A/ Re-execute last command A Answer a call B0 ITU-T V.22/V21 B1 Bell212/103 Dn Dial Modifier EO Command echo off E1 Command echo on HO Disconnect call H1 Go off-hook IO Report product code I1 Report checksum I2 Report OK I3 Report model version I4 Report product name I5 Report 022-Cntry code I6 Report code revision L0 Set low spkr volume L1 Set low spkr volume L2 Set med spkr volume L3 Set high spkr volume M0 Spkr off always M1 Spkr on until DCD M2 Spkr on always M3 Spkr on during answer On Return to On-Line Data Mode P Force pulse dial(in dial string) Q0 Allow result codes Q1 Inhibit result codes Sn Set S-Register Sn? Report value of S-Register T   Force DTMF (Tone) Dialing V0 Terse result codes V1 Verbose result codes W0 Report DTE speed W1 Report DTE, DCE and EC protocol W2 Report DCE Speed X0 Report basic call progress X1 Report basic call progress X2 Report basic call progress codes and connect speeds X3 Report basic call progress result codes X4 Report all call progress result codes Z0 Soft rest & restore profile 0 Z1 Soft rest & restore profile 1	&C0 Force DCD on &C1 DCD follow CXR &D0 Ignores DTR &D1 Enters command mode when ON-to-OFF transition is detected on DTR &D2 ON-to-OFF of DTR hangs up, assumes command state and disables auto answer(Default) &D3 On-toOFF of transition of DTR causes the modem to soft reset. (Same as ATZ command issued) &F0 Restore factory profile 0 &F1 Restore factory profile 1 &K0 Disable flow control &K3 Enble RTS/CTS flow control &K4 Enble Xon/Xoff flow control &K5 Transparent Xon/Xoff flow control &K6 Enable both RTS/CTS and Xon/Xoff (default for FAX) &M0 Set direct Async mode &M1 Set sync connect with async off line cmd mode. &M2 Set sync w/Dial on DTR &M3 Set sync connect with async off-line command mode and enable DTR to act as Talk/Data switch. &Q0 Set direct async mode &Q1 Set sync connect w/ async command mode &Q5 Attempt EC connection &Q6 Selects Asynch in normal mode &R0 CTS Follows RTS &R1 CTS always True-follows flow control &S0 DSR always True &S1 DSR follows V.25 rules &V Display active config &V1 Display last connection stats &W0 Store NVRAM profile 0 &W1 Store NVRAM profile 1 &Y0 Recall Pfl 0 on pwr up &Y1 Recall Prfl 1 on pwr up &Zn=x Store dial string x (1-35 chrs) to location n (0 -3)	%C0 Disable data compression %C1 Enable MNP5 %C2 Enable V.42bis(err comp) %C2 Enable V.42bis and MNP5 %E0 Disble LQM & auto retrain %E1 Enble LQM & auto retrain %E2 Enable LQM & fallbk-fwd %L Report rec'd signal level %Q Report line signal quality \N0 Select normal/buffered mode \N1 Select Direct mode(upon connect, modem DTE assumes the connection speed) \N2 Select reliable link mode \N3 Select auto reliable mode \N4 Force LAPM mode \N5 Force MNP mode \Vn Enables/Disables single line connect message +MS Selects modulation -TRV Tip & Ring Voltage -STE Set Tele Extension operation

 

GENERAL

This paper lists the more common 'AT' DATA  commands used in several different modems. These commands are oriented to Asynchronous Data Transfer while synchronous data, voice and fax may not be covered here.  Enclosed commands are mostly defined by Conexant (Rockwell) based modems.  Many of these commands are common and may be functional in products such as 3Com (US Robotics), Hayes, Multitech and others.

If you would like a command added, clarified or corrected, please feel free to me with any suggestions or questions.

 

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MODEM OPERATION MODES

There are two basic modes of operation for modems;

·          Command Mode

·          Data Mode.

 

COMMAND MODE: (Commonly referred to as the off-line or IDLE condition)

 

The modem is always in the Command Mode when it is not connected to another modem.. The modem may also be in the Command Mode while connected to another modem by entering the +++ sequence.  Any data given to the modem during the Command Mode is not sent to the remote (far end) modem but is used for controlling the options.

 

DATA MODE: (Also known as the on-line or connected condition)

 

The modem is in the Data Mode when it is connected to another modem, and not in the Command Mode.  When connected, all characters sent are interpreted as data and are sent to the remote modem.

 

While connected, you may from the Data Mode to the Command Mode by entering the escape characters bracketed by a one second delay:

 

{1sec delay} +++ {1sec delay}

 

When modem returns 'OK', it has entered into the Command Mode and the characters you send do not get transmitted to the remote modem. (The +++ character string is settable in the S2 register). When connected and in the Command Mode, you may return to the Data Mode by entering ATO<cr>.

 

Command Buffer:

 

The command buffer length is 39 characters maximum per entry. The AT, <cr>, line feed, commas, spaces, back spaces, and dashes are not counted as characters. Characters are NOT case sensitive.  Command strings longer than the 39 character buffer maximum will post an ERROR message and commands will not be executed. The back space can be used to edit typographical errors.

 

"AT" Format

AT command format is:

• ATXn <cr> where “X” is the option and "n" equals the parameter, usually 0 or 1.

• An omission of the 'n' parameter assumes the n=0

• Multiple commands may be inserted in a single string.

  • A string with multiple commands ... AT&F AT&W ATW2<cr> equates to AT&F&WW2<cr>

• All strings must begin with AT and terminate with a <cr> 'Carriage Return' (Except for the 'A/'). 

• AT commands may interact with S-Registers.

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AT Commands:

A/ Repeat previous command. The prefix AT and terminator <cr> is not needed with this command

 

A  Answer Mode: Modem immediately enters the Answer mode, goes off hook and sends answer tone. (Just like responding to an incoming ring signal.) Any character entered to the modem from the DTE during negotiation will abort the negotiation return to the Idle State and await the next command.

Bn Select CCITT or Bell standard for lower speeds.

B0 CCITT operation at 300bps(V.21) or 1200bps(V.22A/B)

B1 Bell operation at 300bps (Bell103) or 1200bps(Bell212) (default)

 

D         Dial

           Valid commands that may follow the D (Dial) command:

0-9    Dial DTMF digits 0 to 9

 

A–D   Dial DTMF digits A, B, C, and D

 

P        Select pulse dialing; affects current and subsequent dialing until changed

 

T        Select tone dialing; affects current and subsequent dialing until changed

 

S=r    Dial stored number r (see &Z for storing numbers) 

 

!        Flash: go on-hook for a time defined by S29 then go off hook 

 

W      Wait for dial tone. If no dial tone is detected within the time specified by S7, the modem aborts the dialing, goes on-hook, and generates an error message. If dial tone is detected during the S7 time, dialing continues immediately.

 

@      Wait 5 seconds of silence before proceeding with next dialing string and then complete handshake sequence. 

 

,         Pause. The modem pauses for a time specified by S8 before dialing subsequent digits.

          Most often used when dialing an outside line through a PBX.

;         Return to command mode after processing command.

^       Disable calling tone transmission; applicable to current dial attempt only.

 

En Command echo - Controls the echo of characters during command mode.

E0 Disables command echo.

E1 Enables command echo (default).

 

 

Hn Disconnect (hang up) - Initiates the disconnect sequence

H0 Go ON-HOOK, i.e. disconnect or hang up (default).

H1 Go off-hook, i.e. connect to the phone line

 

 

In Modem Identification - Ability to read some modem firmware information.

I0 Reports product code (either 33600 or 56000).

I1 Reports 255 if the pre-stored checksum value is FFh.

I2 Reports OK (for software compatibility).

I3 Reports the Firmware version of modem

           Example : V3.000-V90_2M_DLS

I5 Reports the country code setting.  i.e. 022  (North America)

I6 Reports the ROM version of modem IC

 

 

Ln Speaker volume (see also Mn command)

L0 Off or low volume.

L1 Low volume (default).

L2 Medium volume.

L3 High volume.

 

 

Mn Speaker control

M0 Speaker is always off

M1 Speaker is on during call establishment, and turns off upon carrier detection (default).

M2 Speaker is always on.

M3 Speaker is off during dialing and when receiving carrier, but on during answering.

 

 

On Return to On Line Data Mode

O0 Enters the mobem back to the on-line data mode without a retrain. Generally use in conjunction with the escape (+++) to the command modem.  If a connection exists, this command returns the modem from the command state to the data state without losing the connection.

O1 Enters the on-line data modem with a retrain before returning to the on-line data mode.

O2 Fast retrain without speed change (used for diagnostic purposes only)

O3 Renegotiate rate without speed change (used for diagnostic purposes only)

O4 Renegotiate rate down one speed (used for diagnostic purposes only)

O5 Renegotiate rate up one speed  (used for diagnostic purposes only)

 

 

Qn Quiet results codes control

Q0 Enables result codes to the DTE (default).

Q1 Disables result codes to the DTE.

 

 

Sn Read/Write to S-registers - User selects an S-Register, performs an S-Register read or write function, or reports the value of an S-Register.

Sn Establishes S-register "n" as the last register accessed.

Sn= v Sets S-register "n" to the value "v"

Sn? Reports the value of S-register "n".

 

The parameter n can be omitted, in which case the last S-Register accessed will be assumed. The S can be omitted for the AT=<cr> and AT?<cr> in which case the last S-Register accessed will be assumed.

 

Inputs and outputs are always in decimal format.  If the parameter n or v is outside the valid range, the modem will return ERROR.  

Note:  In some cases writing to the S register may appear to be accepted but the value will not actually be written, also some S-Parameters are read-only.

 

Vn Result output code format - V0(Terse) responds as numbers, V1(Verbose) responds with words

V0 Enables short-form (terse) result codes.

V1 Enables long-form (verbose) result codes (default).

 

 

Wn Error correction message control

W0 Upon connection, the modem reports only the DTE (Port) speed (e.g., CONNECT 38400). Subsequent responses are disabled (default).

W1 Upon connection, the modem reports the line (modem to modem) speed, the error correction protocol, and the DTE speed. Subsequent responses are disabled.

W2 Upon connection, the modem reports DCE speed (e.g., CONNECT 33600) ie the line (modem-modem) speed. Subsequent responses are disabled.

 

 

Xn Extended Result Codes

X0 Ignores dial & busy tone. Sends CONNECT message when a connection is established by blind dialing.

X1 Disables monitoring of busy tones; sends only OK, CONNECT, RING, NO CARRIER, ERROR. If busy tone detection is enforced and busy tone is detected, NO CARRIER will be reported instead of BUSY. If dial tone detection is enforced or selected and dial tone is not detected, NO CARRIER will be reported instead of NO DIALTONE.

X2 Disables monitoring of busy tones. Sends only OK, CONNECT, RING, NO CARRIER, ERROR, NO DIALTONE, and CONNECT XXXX. If busy tone detection is enforced and busy tone is detected, NO CARRIER will be reported instead of BUSY. If dial tone detection is enforced or selected and dial tone is not detected, NO CARRIER will be reported instead of NO DIALTONE.

X3 Enables monitoring of busy tones; sends only OK, CONNECT, RING, NO CARRIER, ERROR, NO DIALTONE, and CONNECT or CARRIER XXXX. If dial tone detection is enforced and dial tone is not detected, NO CARRIER will be reported.

X4 Enables monitoring of busy tones; sends all messages. (Default.)

 

 

Zn Soft reset and restore profile

Z0 Soft reset and restore stored profile 0.(Default)

Z1 Soft reset and restore stored profile 1.

 

 

&Cn Data Carrier Detect (DCD) option

&C0 DCD is forced ON at all times.

&C1 DCD will operate normally, i.e. comes ON when carrier from the remote modem is detected. (default).

 

 

&Dn DTR option

&D0 Modem ignores the state of DTR from host.

&D1 An ON-to-OFF transition of DTR causes modem to enter command mode.  If on line, modem will remain on line.

&D2 Upon detecting ON-to-OFF transition of DTR, modem hangs up, assumes command state and disables auto-answer (Default).  <FYI, If DTR is off during a dial attempt, modem will negotiate as normal, but when carrier is detected, modem will immediately disconnect.>

&D3 ON to OFF transition causes the modem to perform a soft reset.  It is the same as an assertion of ATZ command.

 

 

&Fn Restore factory configuration (profile)

&F0 Recall factory profile 0.(Default)

&F1 Recall factory profile 1.

 

 

&Kn Flow control - This is an important command that deserves commentary:

This command determines the method of controlling the flow of data between the Local PC and the Local modem. In most applications, the speed between the PC and the modem (DTE Speed) is different than actual connected speed between the modem (DCE Speed).  If the DCE speed is slower, (and usually is the case) the data will be sent into the modem faster than the modem can send it to the remote modem. In these cases, the Local Modem must tell the Local PC to stop sending data until the modems buffer can empty.  When the buffer is almost full, the modem will send an Xoff (or turn OFF CTS) telling the Local PC to stop sending data. When the local modems buffer is empty again, the local modem will then send an Xon (or turn ON CTS)

&K0 Disables flow control.

&K3 Enables RTS/CTS flow control (default for data modes). Flow control is active in both sending and receiving directions

&K4 Enables XON/XOFF flow control. Flow control is active in both sending and receiving directions

&K5 Supports transparent XON/XOFF flow control.  Xon/Xoff characters sent from the system will be processed for flow control and also sent to the remote modem.  Flow control is active in both sending and receiving directions.

&K6 Enables both RTS/CTS and XON/XOFF flow control (default for fax modes).

 

 

&Mn Select Sync/Async Operation

&M0 Selects direct asynchronous operation (flow control is disabled for direct mode connections)

&M1 Sets sync connect with async off line command mode

&M2 Sets sync connect w/Dial on DTR

&M3 Set sync connect with async off-line command mode and emable to act as Talk/Data switch

 

 

&Qn Select Operation Mode

&Q0 Selects direct asynchronous operation (flow control is disabled for direct mode connections)

&Q1 Synchronous setting - ref to manual

&Q2 Synchronous setting - ref to manual

&Q3 Synchronous setting - ref to manual

&Q5 Attempt an error corrected link (default) Value 101b is written to S27 bits 3,1, and 0 respectively

&Q6 Selects asynchronous operation in normal mode (allows speed buffering and flow control but no error correction).  Value 110b is written to S27 bits 3,1 and 0

 

 

&Rn RTS/CTS function-Selects the control and operation of CTS

The operation of this signal is effected by &K command (Parameter is written to S21 bit 2.)

&R0 In synchronous mode CTS tracks the state of RTS with delay defined by S26.  In async mode, CTS is normally ON and will turn OFF only if required by flow control

&R1 In synchronous mode, CTS is always on (RTS transition are ignored).  In async mode, CTS is normally ON and will turn OFF only if required by flow control.

 

 

&Sn DSR override

&S0 DSR forced ON continuously (default).

&S1 DSR becomes active after answer tone has been detected and inactive after carrier has been lost.

 

&V Display current configuration and stored profiles of most settings.

 

 

Useful for troubleshooting.  Returns a list of several specifics of the last connection.  Most information is intended for DSP development but some info may be helpful on the system level.

 

Examples:

 

TERMINATION REASON............................  LOCAL REQUEST

LAST TX rate .........................................   26400

HIGHEST TX rate  ..................................   26400

LAST RX rate   .......................................   49333

HIGHEST RX rate   .................................   49333

PROTOCOL  ...........................................   LAPM

COMPRESSION   ....................................   V42Bis

Line QUALITY   ......................................   038

Rx LEVEL   .............................................   015

Hightest Rx State  .................................   67

Highest Tx State   .................................   67

EQM Sum   ............................................   00B4

Min Distance  ........................................   0000

RBS Pattern  .........................................   00

Rate Drop  ............................................   00

Digital Loss   ........................................   2000

LOCAL Rtrn COUNT  ..............................   00

Remote Rtrn Count................................   00

Flex  .....................................................   9481814347c4

 

Refer to the manual for further details.

 

 

&Wn Saves current configuration to location 'n'. Will save DTE speed, parity settings, AT commands, and S Registers

&W0 Save the current configuration as profile 0.

&W1 Save the current configuration as profile 1.

 

&Yn Selects which previously stored profile (&Wn) will be recalled with an ATZ or 'power on' reset. (Note: both AT commands and S registers are saved in this setting)

&Y0 The modem uses profile 0.

&Y1 The modem uses profile 1.

 

 

&Zn Stores telephone number in NV memory

Example: &Zn =x Stores telephone number 'x' in location 'n'

 

 

%Cn Enable or disable data compression

%C0 Disables data compression.

%C1 Enables MNP 5 data compression negotiation.

%C2 Enables V.42 bis data compression. Sets S46 bit 1.

%C3 Enables V.42 bis and MNP 5 data compression. (default.)

 

%En Line quality monitor and auto-retrain for fallback/fall-forward.  If enabled, the modem will attempt a retrain for 30 seconds, if unsuccessful, will cause disconnect 

%E0 Disable line quality monitor and auto-retrain

%E1 Enable line quality monitor and auto-retrain.

%E2 Enable line quality monitor and fallback/fall-forward. (default)

 

 

%L Return Line signal level  - Returns a value that indicates the received signal level seen on the modems receiver IC (DAA Dependent).

 

Example; 009 = –9dBm... 043 = –43dBm etc.

                          (number closer to 0 <zero> is better)

Note:  The FCC requires that modems not transmit higher than -9dbm.  Typical PCM modems transmit appx -15 to -20dbm - this value is auto adaptive and not accessible to the design.  Dial modems absolute min receive level is -41 to-43dbm (and that is a very dicey level).

 

For example, assume the remote modem is transmitting at -20dbm and there is a 15db loss in the line.  The %L will return  035  (-35dbm receive level)  Typical phone lines have about 10 to 20 db loss in the line, but that could vary greatly.

 

%Q Line signal quality (DAA dependent)

Reports line signal quality. Returns higher order byte of the EQM value. Based on EQM value, retrain or fallback/fall-forward may be initiated if enabled by %E1 or %E2.

 

 

\N Controls the preferred error correcting mode negotiated in a data connection.

  

THIS IS A CONFUSING, THEREFORE DANGEROUS, COMMAND IT IS RECOMMENDED TO KEEP THE DEFAULT \N3 UNLESS YOUR ABSOLUTELY SURE OF YOUR NEEDS.

 

\N0 Selects normal speed buffered mode (disables error-correction mode).  (Forces &Q6)

\N1 Serial interface selected - Selects direct mode and is equivalent to &M0, Forces &Q0.  
Upon connection, the modem serial port will assume the connection speed... i.e. if both modems negotiate a speed at 2400bps, the modem port will assume that speed.  Be careful with this command for your computer serial port (DTE) may end up different than the modem port and you will appear to send or receive garbage.

\N2 Selects reliable (error-correction) mode.  The modem will first attempt a LAPM connection and then an MNP connection.  Failure to make a reliable connection results in the modem hanging up.  (Forces &Q5, S36=4, and S48=7)

\N3 Selects auto reliable mode.  This operates the same as \N2 except failure to make a reliable connection results in falling back to the speed buffered normal mode.  (Forces &Q5, S36=7 and S48=7)  (default.)

\N4 Selects LAPM error-correction mode.  Failure to make a LAPM error-correction connection results in modem hang-up. (Forces &Q5 and S48=0)  Note:  The -K1 command can override the \N4 command.

\N5 Selects MNP error-correction mode.  Failure to make an MNP error-correction connection results in the modem hanging up. (Forces &Q5, S36=4, and S48=128)

 

\Vn Enables/Disables single line connect message . 

\V0 Connect messages are controlled by the command settings X, W and S95

\V1 Connect messages are displayed in the single line format described below subject to the command settings V (Verbose) and Q (Quiet).  In Non-Verbose mode -aka'Terse' mode (V0), single line connect messages are disabled and the single number result code is generated for CONNECT DTE

When single line connect messages are enabled, there are no CARRIER, PROTOCOL (+ER:), or COMPRESSION (+DR:) messages apart from the fields described below.

The single line connect message format is:

 

CONNECT <DTE Speed>/<Modulation>/<Protocol>/<Compression>/<Line Speed>

Where:

DTE Speed =           DTE speed, e.g., 57600.

Modulation =          “V92” for V.92 modulation.

                               “V90” for V.90 modulation.

                               “V34” for V.34 modulation.

                               “V32” for V.32 or V.32bis modulation.

       Note: Modulation is omitted for all other modulations.

Protocol =               “NONE” for no protocol.

                               “ALT” for Microcom Network Protocol.(MNP)

                               “LAPM” for LAP-M protocol.

 

Compression =       “V44” for V.44 compression.

                               “V42B” for V.42bis compression.

                               “ALT” for Microcom MNP5 compression.

       Note: Compression is omitted if protocol is NONE.

Line Speed =           Asymmetric rates are displayed as “/rate:TX/rate:RX”, e.g., /1200 TX/75 RX.

                                Symmetric rates are displayed as a single DCE rate, e.g., 14400.

AT+MS Command-(Found in Conexant based products)

This powerful command is useful to control specific modulations or connection (DCE) speeds. It is highly recommended this command be changed only by knowledgeable users.

 

*The +MS command operates differently depending on firmware revision of the Conexant Chip set.

 

ATI3 Firmware Versions 3.x or higher: (Releases after V.90<56k>)

 

+MS Modulation Selection

The +MS command may be used to select or force a specific modulation, enable or disable automode and set the lowest and highest connection rate:

 

+MS is comprised of six (6) parameters:

• Carrier <carrier> See chart below

• Automode <automode>: 0 or 1

• Minimum Transmit Rate <min_tx_rate>: See chart below

• Maximum Transmit Rate <max_tx_rate>: See chart below

• Minimum Receive Rate <min_rx_rate>: See chart below

• Maximum Receive Rate <max_rx_rate>: See chart below

 

Syntax:  The +MS command (commas (,) and carriage return <cr> are required):

+MS=<carrier>,<automode>,<min_tx_rate>,<max_tx_rate>,<min_rx_rate>,<max_rx_rate>,<cr>

 

To read the current settings enter: AT+MS?<CR>

A typical response: +MS: V92,1,300,33600,300,56000

 

Meaning:

V92(V.92 modulation), 1( Automode enabled), 300(min_tx_rate) 48000( max_tx_rate) 300(min_rx_rate), 56000(max_rx_rate)

 

 

<automode> A numeric value which enables or disable automatic modulation negotiation (e.g., ITU-T V32bis Annex A or V.8)

0 = Automode disabled – Fixed Modulation

1 = Automode enabled – Automatically selected speed and modulation (Default.)

 

-TRV Reports the Voltage across Tip and Ring

 

Example:   AT-TRV<cr>

Response:  1.4    <no line is connected>

                    54    <line is connected.>

Note:  The voltage measurement is read on the opposite side of a diode bridge, so the modem compensates for the voltage drop across 2 diodes.  Therefore, if no Telco line is connected, the modem will report 1.4v, if the Telco is present and no devices are off hook, the modem will report 54v.

-STE Set Telephony Extension operation

Enables/Disables 'Line In Use', 'Extension Pickup', and 'Remote Hangup' detection features

Example:   AT-STEn<cr>

n Value: 0-7   (0=default)  Decimal number corresponding the the selected bit mapped options defined as follows:

Bit 0  Line In used detection enable/disable

Bit 1  Extension Pickup detection enable/disable

Bit 2  Remote Hangup detection enable/disable

 

 

For more detailed information see the -STE command in the Conexant manual linked below

 

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End of AT commands

Here is the complete Conexant Manual for ALL available AT Commands and S-Registers. 

Doc. No. 102184B - July 1, 2003

 

End