AT Command

* AT — This prefix begins all but two commands you issue to the modem locally, and tells the modem “ATtention! commands to follow”.
* D — Dial. Use the D command to dial a telephone number from the command line. The format of the command is as follows:
ATD [string]

The string parameter can contain up to 45 characters, the phone number and dial modifiers. The dial modifiers instruct a modem how to place the call. Do not use any added characters, such as parentheses or hyphens in the phone number.

* +++ — Escape Character Sequence. After you have connected to another modem, you may need to return to command mode to adjust the modem configuration, or more commonly, to hang up. To do this leave your keyboard idle (press no keys) for at least one second, then press “+” three times. This is one of the two commands that do not use the AT prefix, or a carriage return to enter. After a moment, the modem will respond with OK indicating you have been returned to Command mode.
* A/ — Repeat. This command does not use the AT prefix nor does it require a carriage return to enter. Typing this command causes the modem to repeat the last command line entered, and is most useful for redialing telephone numbers which are busy.
* &Fn — Factory Defaults. This command (in which n=0 or 1) returns all parameters to the selected set of factory defaults.
* H — Hang Up. This command tells the modem to go “on-hook”, or to disconnect the telephone line.
* O — On-Line. This command returns the modem to the on-line mode and is usually used after the escape sequence (+++) to resume communication.
* Zn — Reset Modem. This command (in which n=0 or 1) resets the modem to the configuration profile stored in non-volatile memory location 0 or 1

Syntax: ATD{dial modifier} 1234567 [Enter]

Basic dial modifiers are:

* P — Pulse dialing. Also known as rotary dialing, this dial modifier follows the D command and precedes the telephone number to tell the modem to dial the number using pulse service.
* T — Tone dialing. This modifier selects the tone method of dialing using DTMF tones. Note: Tone and pulse dialing can also be combined in a dial command line when both dialing methods are required.
* ; — Resume command mode after dialing. If you need to dial a number that is too long to be contained in the command buffer (45 characters for the D command), use the (;) modifier to separate the dial string into multiple dial commands. All but the last command must be end with the ; modifier.
* , — Pause While Dialing. The comma (,) dial modifier causes the modem to pause while dialing. The modem will pause the number of seconds specified in S-Register S8 and then continue dialing. If a pause time longer than the value in S-Register S8, it can be increased by either inserting more than one (,) in the dial command line or changing the value of S-Register S8. In the following example, the command accesses the outside (public) telephone line with the 9 dial modifier. Because the comma (,) dial modifier is present, the modem delays before dialing the telephone number 5551212. Ex: ATD 9, 5551212 [Enter]
* ! — Using the Hook Flash. The exclamation mark (!) dial modifier causes the modem to go on-hook (hang up) for one-half second and is equivalent to holding down the switch-hook on your telephone for one-half second. This feature is useful when transferring calls.
* W — Wait for a Subsequent Dial Tone. The W dial modifier causes a modem to wait for an additional dial tone before dialing the numbers that follow the W. The length of time the modem waits depends on the value in S-Register S7. The modem can be instructed to dial through PBXs (Private Branch Exchanges) or long-distance calling services that require delays during dialing. This can be done with the W command to wait for a secondary dial tone or with a comma (,) command to pause for a fixed time and then dial. Ex: ATDT 9 W 1 2155551212 [Enter]

Making a Call

The following examples show how to place a call using several of the dial modifiers.

ATD 1234567

The modem dials the telephone number 1234567 and then waits for a carrier from a distant, or remote modem. If no carrier is detected within a given time (as defined by the initial settings in S-Register 6), then the modem automatically releases the line and sends a NO CARRIER result code. If a carrier is detected, the modem gives a CONNECT result code and goes on-line, allowing communications with the remote modem. The connection between the two modems ends when any of the following occurs causing the modem to hang up, return to command mode, and send the NO CARRIER response:

* The local modem loses the carrier signal from the remote modem.
* The Hang Up command (H) is sent.
* The DTR interface signal is dropped between the local DTE and modem when the &D2 or &D3 command is in effect.

AT &F1DT9,P5551234 [Enter]

This command restores the factory default settings, dials, using tones, a 9 to access an outside line, pauses briefly, then pulse dials the number 555-1234.

Manually Dialling with the Telephone

To manually dial the phone, you should be in your communications software’s command mode.

1. Lift the receiver of the telephone and dial the number you wish to call.
2. Type ATH1 and press [Enter] to connect the modem and then hang up the receiver.
3. Type AT0 and press [Enter] to tell the modem to go on line.
Manual Answer

When the automatic answer feature (S-Register S1) is not being used, incoming calls can be answered manually by typing:

ATA [Enter]

When an incoming call is received. The modem will answer the incoming call and [Enter] the on-line mode.
Controlling the Modem — Overview

This reference guide has been published in order to provide you with the information needed to set the parameters and variables that are used to control the operation of your modem.


To transmit or receive data, the modem must be in the on-line state. When placing a call, the modem is put on-line with the dial command. At the remote end, the modem goes on-line when it is instructed to answer a call automatically by setting the S-Register S0 equal to any number greater than 0 and less than 255. You can also perform this function with the ATA command.


After a connection has been established with a remote modem, you can return to command mode without breaking that connection by typing the escape sequence. The escape sequence consists of three characters (+++). It is not necessary to begin this sequence with the attention code, or by pressing [Enter] after typing the escape code.


The modem can be returned to the on-line state after the escape sequence has been issued. To return the modem to the on-line state, issue the ATO command. To return the modem on-line and then initiate an equalizer retrain sequence, use the ATO1 command.


Each command sent to the modem remains in the command buffer until the next command is sent, or until power to the modem is turned off. To repeat the last command issued, type the command A/. The A/ command is not preceded by the AT characters or followed by pressing [Enter]. See the command reference for more information.


Some command require a parameter to completely define them. If a parameter is omitted from a command that requires one, the command will use the default value.


A response is displayed on your screen by the modem, indicating the result after it processes, or tries to process a command. These result codes display the status of the modem, or the progress of a call sequence, and can take the form of either words or digits. The default consists of word responses that are defined by the ATV1 command. To receive digit responses rather than words, use the ATV0 command. To disable responses entirely, use the ATQ1 command.


All control commands to the modem are prefixed with either AT or at and terminated by a carriage return (Enter). Mixed case set (“At” or “aT”) is not allowed. The “AT” sequence is called the “ATTENTION COMMAND”. The Attention command precedes all other commands except RE-EXECUTE (A/) and the ESCAPE (+++)code.

Several commands which are preceded by AT can be entered in a single line followed by the carriage return character. Spaces can be inserted between commands to increase readability, but will not be stored in the command buffer, the size of which is 255 characters. The Backspace character can be used to erase mistakes but is not saved as part of the contents of the command buffer in terminal applications. Unsupported commands will be logged and an “OK” or “ERROR” will be returned.

Commands will only be accepted by the modem once the previous command has fully executed. A command line may be aborted at any time by entering “CTRL X”. The AT sequence may be followed by any number of commands in sequence, except for commands such as Z, D, or A. Commands following Z, D, or A on the same command line will be ignored. The maximum number of characters on any command line is 56 (including A and T).

AT Command Reference Summary
%Cn — Enable/Disable Data Compression
%En — Auto-Retrain control
&Cn — DCD Control
&Dn — DTR Option
&Fn — Recall Factory Profile
&Gn — Select Guard Tone
&Jn — Telephone Jack Control
&Kn — Data Flow Control
&Qn — Communication (Sync/Async Mode)
&Rn — RTS/CTS (Hardware) Flow Control
&Tn — Test Mode
&V — View Configuration
&Wn — Store User Profile
&Yn — Default User Profile
&Zn=x — Store Phone Number
)Mn — Cellular Power Level Adjustment
*Hn — Link Negotiation Speed
+++ — Escape Sequence
+MS — Select Modulation
:En — Compromise Equalizer Setting
? — Read Currently Selected S Register
@Mn — Initial Cellular Power Level Setting
\An — Select Maximum MNP Block Size
\Bn — Transmit Break
\Gn — Modem to Modem (Software) Flow Control
\Ln — Select MNP Block/Stream Mode
\Nn — Protocol Negotiation Selection
A — Answer
A/ — Re-execute Command
Bn — CCITT or Bell Selection
Cn — Carrier Control
Dn — Dial
En — Command Echo
Fn — Select Modulation
Hn — Disconnect (Hang-up)
In — Identification
Ln — Speaker Volume
Mn — Speaker Control
Nn — Automode Enable (Automatic Line Speed Detection)
On — Return to On-Line Data Mode
P — Set Pulse Dial Default
Qn — Result Code On/Off
Sn — Select a Specific S Registe
Sn=x — Write an S Register Value
Sn? — Read an S Register
T — Set Tone Dial Default
Vn — Result Code Format
Wn — Negotiation Progress (Connect Message) Control
Xn — Extended Result Code
Yn — Long Space Disconnect
Zn — Modem Reset

Basic Commands
+++ (Escape Sequence)

The escape sequence causes the modem to go to the off-line command state from the on-line data state. After this escape sequence, the modem can accept user’s AT commands. The escape sequence consists of three escape code that is defined by S-Register 2 (default value: decimal 43(+)).

Do not enter any character before and/or after the “+++” for a guard time specified by S-Register 12 (default: 1 second). The duration between escape codes must also be within the guard time. After the modem recognizes a valid escape sequence, an “OK” result code is returned. If an escape sequence is valid, the escape code is transmitted to a remote modem. The ATO command is used to go back to on-line data state.

For example:
ATD 0123456 [enter]
[data] [—-]
( 1 sec pause )
+++ (Without 1 sec pause between escape codes)
( 1 sec pause )
OK (On-line command state)
ATH0 [CR] (Disconnect the line)

A/ (Re-execute Command)

This command re-executes the previous command processed by the modem. This command will be useful to re-dial without entering a dial string when a line is busy or unanswered. This command is not preceded by “AT”, or followed by [Enter].

In (Identification)

This command instructs the modem to return its product identification information.

* I0 — Returns the product code.
* I1 — Reports the 3 digits pre-computed ROM checksum code.
* I2 — Calculates a checksum of the modem firmware ROM and indicates OK or ERROR for the checksum validity.
* I3 –Returns the modem ROM version.
* I4 — TBD
* I5 — TBD
* I6 — Returns the modem data pump model.
Zn (Modem Reset)

This command resets the modem and recalls the stored configuration as defined at power on time.

* Z0 — Reset and recall stored user profile 0.
* Z1 — Reset and recall stored user profile 1.
&Fn (Recall Factory Profile)

This command reloads the factory default profile.

* &F0 — Recall Factory Profile 0. Factory Profile 0 contains the default values from the modem chipset supplier.
* &F1 — Recall Factory Profile 1. Factory Profile 1 contains the default values defined by the product manufacturer.
&Jn (Telephone Jack Control)

This command is only included for compatibility and performs no function. The value is written into S-Register 21.

&V (View Configuration)

This command displays the current active configuration, stored user profiles, and the first four stored telephone numbers. Applications may change these profile.

If the modem’s non-volatile memory is detected as defective by the modem’s NVRAM test, the modem will display NVRAM FAILED OR NOT INSTALLED

&Wn (Store User Profile)

This command stores the current, active configuration including S-Registers into non-volatile memory as stored user’s profile 0 or 1. Storable parameters can be viewed by &V command. Stored parameters can be recalled into active configuration by Zn command or at power on.

* &W0 — Store active configuration as user’s profile 0.
* &W1 — Store active configuration as user’s profile 1.
&Yn (Default User Profile)

This command selects which of two user’s profiles will be loaded into the active configuration following Power on Reset.

* &Y0 — Selects power up configuration as user’s profile 0.
* &Y1 — Selects power up configuration as user’s profile 1.
&Zn=x (Store Phone Number)

This command stores up to 4 telephone number dial strings into one of 4 non-volatile memory locations specified by n. This stored phone number can be used for later abridged dialing with the DS=n command.

n: Entry number (range 0-3)
x: dial string less than 45 digits (including dial modifiers)
Speaker Controls
Ln (Speaker Volume)

This command controls the modem speaker volume when the speaker is turned on.

* L0,1 — Selects low speaker volume.
* L2 — Selects medium speaker volume.
* L3 — Selects high speaker volume.
Mn (Speaker Control)

This command selects when the modem speaker will be on or off.

* M0 — The speaker is always off.
* M1 — Enables the speakerduring call establishment, but off once the carrier is detected.
* M2 — The speaker is always on.
* M3 — Disables the speaker during the dialing period and receiving carrier, but on during answering.

Dial Commands
A (Answer)

The modem will go off hook, transmit the answer tone, and wait for a carrier from the remote modem.

Cn (Carrier Control)

This command is included for compatibility only and has no effect other than returning a result code.

Dn (Dial)

Puts the modem into origination mode, allowing it to work as an automatic dialer for connection to another modem. The string n contains the telephone number and the following optional “dial modifiers”.: The string n must be less than 45 characters excluding spaces, hyphens, and parenthesis, which can be used for clarity.

* 0-9 — DTMF digits 0 to 9
* * — The “star” digit (tone dialing only)
* # — The “gate” digit (tone dialing only
* A-D — DTMF digits A, B, C, D.
* J — Perform MNP 10 link negotiation at 1200 bps (this call only)
* K — Enable power level adjustment during MNP 10 link negotiation (for this call only).
* L — Re-dial last number. The L must be immediately after the D with the following characters ignored.
* P — Selects Pulse dialing. Only digits 0-9 can be entered in pulse dial mode.
* R — Reverse dial mode. This command accepted but not acted upon.
* S=n — Dial stored number. Dials the number stored in location n (0-3)
* T — Select tone dialing. Any digit 0-9,*,#,A,B,C,D, etc. may be dialed.
* W — Wait for dial tone. The modem waits for dial tone before processing the dial string.
* , — Pause. Causes the modem to pause for the time specified by S-Register 8 before processing the next character in the dial string.
* ! — Flash hook. This causes the modem to go on-hook for the time defined by the value of S-Register 29, and then return off-hook.
* @ — Wait for silence. The modem will wait for five seconds of silence before dialing the remaining dial string.
* ; — Return to idle state. Modem returns to command mode after dialing a number without disconnecting the call.
* & — Wait for &T “bong” tone for credit card dialing before continuing with the remaining dial string.
Hn (Disconnect)

This command provides switch hook control.

* H0 — Instructs the modem to disconnect or hang-up.
* H1 — Instructs the modem to go off-hook and enter command mode.
P (Set Pulse Dial Default)

This command forces pulse dialing until the next T dial modifier or T command is received. Sets S-Register bit 5.

T (Set Tone Dial Default)

This command forces DTMF dialing until the next P dial modifier or P command is received. Clears S-Register bit 5.

Yn (Long Space Disconnect)

This command determines whether the modem hangs up when it receives a long space signal (greater than 1.6 seconds) from the remote modem. If enabled, the modem will send a 4 second space signal to the remote modem before hanging up.

* Y0 — Disable long space disconnect signaling.
* Y1 — Enable long space disconnect signaling.

Serial Port Control

The 28.8(V.34) / 14.4 Kbps Data/FAX Modems can determine the speed, parity, and stop bits from the serial port connection. The modem automatically detects the serial data speed between 300 and 115,200 bps with the following formats:
Data Length Parity Stop Bits Total Length

7 None 2 10
7 Odd 1 10
7 Even 1 10
7 Mark 1 10
7 Space 1 10
8 None 1 10
8 Odd 1 11
8 Even 1 11

The modem also has the capability of automatically adjusting the baud rate to the internal serial port to physical carrier speed. The user application must adjust the baud rate of the internal serial port to it by detecting carrier speed after CONNECT xxxx message. This command setting is valid for reliable (error corrected) link and normal mode connections. The baud rate adjust feature is always active for direct mode connection.

&Cn (DCD Control)

This command controls the behavior of the DCD (Data Carrier Detect) signal of the internal serial port.

* &C0 — DCD is always on.
* &C1 — DCD will track the state of the data carrier from the remote modem.
&Dn (DTR Option)

This command controls the modem response to the serial port’s Data Terminal Ready (DTR) signal. This command interprets the ON and OFF transitions of the DTR signal from the DTE in accordance with the parameters as defined by n.

&Kn (Data Flow Control)

This command determines how the modem controls data flow between the system and the modem. For example, if the speed between the system unit and the modem is 19200 bps, and the speed between the local and remote modem is 2400 BPS, the transmit buffer of the modem is likely to be overflow when the system is sending large amounts of data. To prevent an overflow and subsequent loss of data, the modem either sends a XOFF character or drops the CTS signal to signal that the system should stop data sending. When enough space is available in the modems transmit buffer, the modem either sends a XON character or raises CTS to signal that application could resume data sending.

For binary data transfer CTS/RTS flow control should be selected since the modem cannot distinguish the user’s data from XON/XOFF characters. Flow control is not used for direct mode connection.

* &K0 — Disables flow control.
* &K1 — Error
* &K2 — Error
* &K3 — Enables RTS/CTS flow control. Flow control is active in both sending and receiving direction.
* &K4 — Enables XON/XOFF flow control. Flow control is active in both sending and receiving direction.
* &K5 — Enables transparent XON/XOFF flow control. XON/XOFF character which is sent from the system unit will be processed for flow control and also sent to the remote modem. Flow control is active in both sending and receiving direction.
* &K6 — Enables both RTS/CTS and XON/XOFF flow control.
&Mn (Communication (Asynchronous/Synchronous) Mode)

Determines the DTR operating mode. The modem treats the &M command as a subset of the &Q command. This command is used to choose between asynchronous, synchronous, or direct dial modes while the modem is in the command state. Only Asynchronous mode is supported., and between synchronous and asynchronous data flow when a connection is established.

* &M0 — Selects direct asynchronous mode.
&Rn (RTS/CTS (Hardware) Flow Control)

This command determines how the modem controls CTS (Clear to Send). CTS operation is modified if hardware flow control is selected.

* &R0 — In synchronous mode, CTS tracks the state of RTS. In asynchronous mode, CTS acts according to V.25 handshake.
* &R1 — In synchronous mode, CTS is always ON (RTS transitions are ignored). In asynchronous mode, CTS will only drop if required by flow control.
&Sn (DSR Override)

Data Set Ready Control

* &S0 — Causes DSR signal to be active at all times.
* &S1– Causes DSR signal to be active according to the V.25 protocol.
&Xn (Select Synchronous Clock Source)

Selects the source of the transmission clock for the synchronous mode of operation. The parameter value, if valid, is written to S27 (bits 4 and 5). In asynchronous mode, the transmission and receipt clocks are turned off.

* &X0 — Selects internal timing.
* &X1 — Selects external timing.
* &X2 — Selects slave receiving timing. The transmission clock signal is derived from the incoming carrier.
\Gn (Modem to Modem (Software) Flow Control)

This command enables and/or disables software flow control using XON/XOFF, between your modem and the remote modem. During a reliable (error corrected)reliable connection this setting is ignored.

* \G0 — Disables modem port XON/XOFF flow control
* \G1 — Enables modem port XON/XOFF flow control
\Wn (Split-Speed Operation)

This command determines the split-speed DCE/DTE interface for applications such as ViewData terminals, which require a transmit speed of 75 bps and a receive speed of 1200 bps at the DTE interface.

* \W0 — Disables split-speed mode.
* \W1– Enables split-speed mode.
%Fn (Split-Speed Direction)

This command determines which direction, transmit or receive, has the 75 bps channel and which has the 1200 bps channel. This command is only valid if the “Split-Speed Operation” command has been executed.

* %F1 — Selects 75 tx / 1200 rx
* %F2 — Selects 1200 tx / 75 rx
* %F3 — Selects V.23 half duplex operation
Command Response and Result Codes

These commands control the responses to commands issued the modem.
En (Command Echo)

This command determines whether the modem echoes characters back to the DTEsystem, when in command mode.

* E0 — Inhibits the command echo – If your system application does not expect the echo, use this setting, otherwise, entering “AT” causes your terminal to display “AATT”.
* E1 — Enables the command echo.
Qn (Result Code On/Off)

Used to enable and disable return results codes to the DTE.

* Q0 — Enable the result code.
* Q1 –Disable the result code, OK, ERROR or CONNECT message will not be returned.
Vn (Result Code Format)

This command determines the format of the return result code if result codes are enabled (see Qn command). For example, the long form (word format) returns “OK” or short form (numeric format) returns “0”. The long form format result code is preceded and terminated by both carriage return and line feed characters. The short form format result code is terminated by a carriage return character.

* V0 — Selects result codes in NUMERIC format.
* V1 — Selects result codes in WORD format.
Xn (Extended Result Code)

This command determines which set of responses and calling characteristics are used. This command determines whether the modem recognizes dial tones and busy tones, and what kind of result code should be enabled. When n is 0, 1, or 3, the modem waits for the time specified by S-Register 6 (default 2 seconds) after going off-hook, then dials regardless of the presence or absence of dial tone. Blind dialing is used in some countries where dial tones could very from central office to central office, or for certain PBX’s which generate unique dial tones.

* X0 — The modem does not recognize dial tone and busy tone. The modem does not wait for dial tone, and blind dialing is enabled. The modem returns a CONNECT result code when a connection is established.
* X1 — The modem does not recognize dial tone and busy tone. The modem does not wait for dial tone, and blind dialing is enabled. The modem returns a CONNECT XXXX result code reflecting the serial port speed when a connection is established.
* X2 — The modem does not recognize busy tones, but waits for dial tone before dialing. If dial tone is not detected within 5 seconds, NO DIALTONE result code is returned. The modem returns CONNECT XXXX result code reflecting the serial port speed when a connection is established.
* X3 — The modem does not recognize dial tone. If a busy tone is detected, BUSY result code is returned. The modem does not wait for dial tone, and blind dialing is enabled. The modem returns CONNECT XXXX result code reflecting the serial port speed when a connection is established.
* X4 — If dial tone is not detected within 5 seconds, NO DIALTONE result code is returned. If a busy signal is detected, BUSY result code is returned. The modem returns CONNECT XXXX result code reflecting the serial port speed when a connection is established.


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