Introduction • Data Commands • Fax Commands
AT commands are used to control the operation of your modem. They are so called because each command must be preceded by the characters AT to get the ATtention of the modem.
AT commands can be issued only when the modem is in command mode or online command mode. The modem is in command mode whenever it is not connected to another modem. The modem is in data mode whenever it is connected to another modem and ready to exchange data. Online command mode is a temporary state in which you can issue commands to the modem while connected to another modem. To put the modem into online command mode from data mode, you must issue an escape sequence (+++) followed immediately by the AT characters and the command, e.g., +++ATH to hang up the modem. To return to data mode from online command mode, you must issue the command ATO.
To send AT commands to the modem you must use a communication program, such as the HyperTerminal applet in Windows 95, 98, and NT 4.0. You can issue commands to the modem either directly, by typing them in the terminal window of the communication program, or indirectly, by configuring the operating system or communication program to send the commands automatically. Fortunately, communication programs make daily operation of modems effortless by hiding the commands from the user. Most users, therefore, need to use AT commands only when reconfiguring the modem, e.g., to turn autoanswer on or off.
The format for entering an AT command is ATXn, where X is the command and n is the value for the command, sometimes called the command parameter. The value is always a number. If the value is zero, you can omit it from the command; thus, AT&W is equivalent to AT&W0. Most commands have a default value, which is the value that is set at the factory. The default values are shown in the Data Commands section.
You must press Enter to send the command to the modem. Any time the modem receives a command, it sends a response known as a result code. The most common result codes are OK, ERROR, and the CONNECT messages that the modem sends the computer when it is connecting to another modem. For a table of valid result codes, see Result Codes.
You can issue several commands in one line, in what is called a command string. The command string begins with AT and ends when you press ENTER. Spaces to separate the commands are optional; they are ignored by the command interpreter. The most familiar command string is the initialization string, which is used to configure the modem when it is turned on or reset, or when your communication software calls another modem.
Basic Commands • & Commands • \ Commands • - Commands • % Commands • $ Commands • + Commands • # Commands • Escape Commands
AT - Attention Code
The attention code precedes all command lines except A/ and the escape sequence.
Enter Key
Press the Enter or Return key to execute most commands.
A - Answer
Answers an incoming call before the final ring.
A/ - Repeat Last Command
Repeats the last command string. Do not precede this command with AT. Do not press Enter to execute.
Bn - Communication Standard Setting
| B0 | Select ITU-T V.22 mode when modem is at 1200 bps. |
| B1 | Select Bell 212A when modem is at 1200 bps. Default. |
| B2 | Deselect V.23 reverse channel (same as B3). |
| B3 | Deselect V.23 reverse channel (same as B2). |
| B15 | Select V.21 when the modem is at 300 bps. |
| B16 | Select Bell 103J when the modem is at 300 bps. Default. |
Cn - Carrier Control
| C0 | Transmit carrier always off. (Not supported.) |
| C1 | Normal transmit carrier switching (included for backward compatibility with some software). Default. |
Ds - Dial
Dial telephone number s, where s may up to 40 characters long and include the 0–9, *, #, A, B, C, and D characters, and the L, P, T, W, S, comma (,), semicolon (;), !, @, ^ and $ dial string modifiers.
Dial string modifiers:
| L | Redial last number. (Must be placed immediately after ATD.) |
| P | Pulse-dial following numbers in command. |
| T | Tone-dial the following numbers in the command. Default. |
| W | Wait for a new dial tone before continuing to dial. (X2, X4, X5, X6, or X7 must be selected.) |
| , | Pause during dialing for time set in register S8. |
| ; | Return to command mode after dialing. (Place at end of dial string.) |
| ! | Hook flash. Causes the modem to go on-hook for one-half second, then off-hook again. |
| @ | Wait for quiet answer. Causes modem to wait for a ring back, then 5 seconds of silence, before processing next part of command. If silence is not detected, the modem returns a NO ANSWER code. |
| ^ | Disable data calling tone transmission. |
| $ | Detect AT&T call card "bong" tone. The character should follow the phone number and precede the user's call card number. Example: ATDT1028806127853500$123456789 |
DS=y - Dial Stored Telephone Number
Values: y = 0–3
Dials a number previously stored in directory number y by the &Zy=x command. Example: ATDS=3.
En - Echo Command Mode Characters
| E0 | Do not echo keyboard input to the terminal. |
| E1 | Do echo keyboard input to the terminal. Default. |
Fn - Echo Online Data Characters
| F0 | Enables online data character echo. (Not supported.) |
| F1 | Disables online data character echo (included for backward compatibility with some software). Default. |
Hn - Hook Control
| H0 | Goes on-hook (hangs up). Default. |
| H1 | Goes off-hook (makes the phone line busy). |
In - Information Request
| I0 | Displays default speed and controller firmware version. |
| I1 | Calculates and displays ROM checksum (e.g., 12AB). |
| I2 | Checks ROM and verifies the checksum, displaying OK or ERROR. |
| I3 | Displays default speed and controller firmware version. |
| I4 | Displays firmware version for data pump (e.g., 94). |
| I5 | Displays the board ID: software version, hardware version, and country ID. |
| I9 | Displays the country code (e.g., NA Ver. 1). |
| I11 | Displays diagnostic information for the last modem connection, such as DSP and firmware version, link type, line speed, serial speed, type of error correction/data compression, number of past retrains, etc. |
Ln - Monitor Speaker Volume
| L0 | Selects low volume. |
| L1 | Selects low volume. |
| L2 | Selects medium volume. Default. |
| L3 | Selects high volume. |
Mn - Monitor Speaker Mode
| M0 | Speaker always off. |
| M1 | Speaker on until carrier signal detected. Default. |
| M2 | Speaker always on when modem is off-hook. |
| M3 | Speaker on until carrier is detected, except while dialing. |
Nn - Modulation Handshake
| N0 | Modem performs handshake only at communication standard specified by S37 and the B command. |
| N1 | Modem begins handshake at communication standard specified by S37 and the B command. During handshake, fallback to a lower speed can occur. Default. |
On - Online Return to Data Mode
| O0 | Exits online command mode and returns to data mode (see +++AT<CR> escape sequence ). |
| O1 | Issues a retrain and returns to online data mode. |
| O3 | Issues a rate renegotiation and returns to data mode. |
P - Pulse Dialing
Configures the modem for pulse (non-touch-tone) dialing. Dialed digits are pulsed until a T command or dial modifier is received.
Qn - Result Codes Enable/Disable
| Q0 | Enables result codes. Default. |
| Q1 | Disables result codes. |
Sr=n - Set Register Value
Values: r = S-register number, n varies
Sets value of register Sr to value of n, where n is entered in decimal format. Example: S0=1.
Sr? - Read Register Value
Values: r = S-register number
Reads value of register Sr and displays it in 3-digit decimal form. Example: S2? generates the response 043.
T - Tone Dialing
Configures the modem for DTMF (touch-tone) dialing. Dialed digits are tone dialed until a P command or dial modifier is received.
Vn - Result Code Format
| V0 | Displays result codes as digits (terse response). |
| V1 | Displays result codes as words (verbose response). Default. |
Wn - Result Code Options
| W0 | CONNECT result code reports serial port speed, disables protocol result codes. |
| W1 | CONNECT result code reports serial port speed, enables protocol result codes. |
| W2 | CONNECT result code reports line speed, enables protocol result codes. Default. |
Xn - Result Code Selection
| X0 | Basic result codes (e.g., CONNECT); does not look for dial tone or busy signal. |
| X1 | Extended result codes (e.g., CONNECT 46000 V42bis); does not look for dial tone or busy signal. |
| X2 | Extended result codes with NO DIALTONE; does not look for busy signal. |
| X3 | Extended result codes with BUSY; does not look for dial tone. |
| X4 | Extended result codes with NO DIALTONE and BUSY. Default. |
| X5 | Extended result codes with NO DIALTONE and BUSY. |
| X6 | Extended result codes with NO DIALTONE and BUSY. |
| X7 | Basic result codes with NO DIALTONE and BUSY. |
Yn - Long Space Disconnect
| Y0 | Disables sending or responding to long space break signal on disconnect. Default. |
| Y1 | Enables sending or responding to long space break signal on disconnect. (Not supported.) |
Zn - Modem Reset
| Z0 | Resets modem to profile saved by the last &W command. |
| Z1 | Same as Z0. |
| &B0 | Disables V.32 auto retrain. (Not supported.) |
| &B1 | Enables V.32 auto retrain. Default. |
&Cn - Data Carrier Detect (DCD) Control
| &C0 | Forces the DCD circuit to be always high. |
| &C1 | DCD goes high when the remote modem's carrier signal is detected, and goes low when the carrier signal is not detected. Default. |
&Dn - Data Terminal Ready (DTR) Control
| &D0 | Modem ignores the true status of the DTR signal and responds as if it is always on. |
| &D1 | If DTR drops while in online data mode, the modem enters command mode, issues an OK, and remains connected. |
| &D2 | If DTR drops while in online data mode, the modem hangs up. If the signal is not present, the modem will not answer or dial. Default. |
| &D3 | If DTR drops, the modem hangs up and resets as if an ATZ command were issued. |
&En - XON/XOFF Pacing Control
| &E12 | XON/XOFF pacing disabled. Default. |
| &E13 | XON/XOFF pacing enabled. (&K4 must also be set.) |
|
NOTE: &E13 has no effect if hardware control (&K3) is selected. |
 |
CAUTION: Do not enable pacing unless you are certain that you need it. Some applications may not work if pacing is enabled.
|
&Fn - Load Factory Settings
| &F0 | Loads factory settings as active configuration. |
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NOTE: See also the Z command. |
&Gn - V.22bis Guard Tone Control
| &G0 | Disables guard tone. Default. |
| &G1 | Sets guard tone to 550 Hz. |
| &G2 | Sets guard tone to 1800 Hz. |
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NOTE: The &G command is not used in North America. |
&Jn - Auxiliary Relay Control
| &J0 | The auxiliary relay is never closed. Default. |
| &J1 | Not supported—responds ERROR. |
&Kn - Flow Control Selection
| &K0 | Disables flow control. |
| &K3 | Enables CTS/RTS hardware flow control. Default. |
| &K4 | Enables XON/XOFF software flow control. |
&Mn - Communications Mode
| &M0 | Asynchronous mode. Default. |
| &M1 | Not supported—responds ERROR. |
&Qn - Asynchronous Communications Mode
| &Q0 | Asynchronous with data buffering. Same as \N0. |
| &Q5 | Error control with data buffering. Same as \N3. Default. |
| &Q6 | Asynchronous with data buffering. Same as \N0. |
| &Q8 | MNP error control mode. If MNP error control is not established, the modem falls back according to the setting in S36. |
| &Q9 | V.42 or MNP error control mode. If neither error control is established, the modem falls back according to the setting in S36. |
&Sn - Data Set Ready (DSR) Control
| &S0 | Forces DSR always high (on). Default. |
| &S1 | Lets DSR go high only during a connection. |
&Tn - V.54 Test Commands
| &T0 | Abort. Stops any test in progress. |
| &T1 | Initiates local analog loopback test. |
| &T3 | Initiates local digital loopback test. |
| &T6 | Initiates remote digital loopback test. |
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NOTE: To stop a test, you must use the escape sequence (+++AT) before typing AT&T0. |
&V - Display Current Settings
Displays the active modem settings, including the callback security settings if callback security is enabled. If the setup password has been entered, it also displays the callback security passwords.
&Wn - Store Current Configuration
| &W0 | Stores current modem settings in nonvolatile memory and causes them to be loaded in place of the factory defaults at power-on or following the ATZ command. See also the &F command. |
| &W1 | Clears user default settings from nonvolatile memory and causes the factory defaults to be loaded at power-on or following the ATZ command. |
&Yn - Select Stored Configuration for Hard Reset
| &Y0 | Selects stored configuration 0 on power-up. (For backward compatibility with some software.) Default. |
| &Y1 | Not supported—responds ERROR. |
&Zy=x - Store Dialing Command
y = 0–3 (callback security disabled) or 0–29 (callback security enabled)
x = dialing command string
Stores dialing command string x in memory location y. Dial the stored number using the command ATDS=y. See also the #CBSn command.
\An - Select Maximum MNP Block Size
| \A0 | 64-character maximum. |
| \A1 | 128-character maximum. |
| \A2 | 192-character maximum. |
| \A3 | 256-character maximum. Default. |
\Bn - Transmit Break
n = 0–9 in 100 ms units
Default: 3
In non-error-correction mode only, sends a break signal of the specified length to a remote modem. Works in conjunction with the \K command.
\Gn - Modem Port Flow Control
| \G0 | Returns an OK for backward compatibility with some software. Default. |
| \G1 | Not supported—responds ERROR. |
\Jn - Data Buffer Control
| \J0 | Enables data buffer—serial port speed is independent of connect speed. Default. |
| \J1 | Disables data buffer—serial port speed is forced to the line speed. |
\Kn - Break Control
Controls the response of the modem to a break received from the computer, the remote modem, or the \B command. The response is different for each of three different states:
Data mode. The modem receives the break from the computer:
| \K0 | Enters online command mode, no break sent to the remote modem. |
| \K1 | Clears data buffers and sends break to the remote modem. |
| \K2 | Same as \K0. |
| \K3 | Sends break immediately to the remote modem. |
| \K4 | Same as \K0. |
| \K5 | Sends break to the remote modem in sequence with the transmitted data. Default. |
Data mode. The modem receives the break from the remote modem:
| \K0 | Clears data buffers and sends break to the computer. |
| \K1 | Same as \K0. |
| \K2 | Sends break immediately to the computer. |
| \K3 | Same as \K2. |
| \K4 | Sends break to the computer in sequence with the received data. |
| \K5 | Same as \K4. Default. |
Online command mode. The modem receives a \Bn command from the computer:
| \K0 | Clears data buffers and sends break to the remote modem. |
| \K1 | Same as \K0. |
| \K2 | Send break immediately to the remote modem. |
| \K3 | Same as \K2. |
| \K4 | Sends break to the remote modem in sequence with the transmitted data. |
| \K5 | Same as \K4. Default. |
\Nn - Error Correction Mode Selection
| \N0 | Non-error correction mode with data buffering (buffer mode; same as &Q6). |
| \N1 | Direct mode. |
| \N2 | MNP reliable mode. If the modem cannot make an MNP connection, it disconnects. |
| \N3 | V.42/MNP auto-reliable mode. The modem attempts first to connect in V.42 error correction mode, then in MNP mode, and finally in non-error-correction (buffer) mode with continued operation. Default. |
| \N4 | V.42 reliable mode.If the modem cannot make a V.42 connection, it disconnects. |
| \N5 | V.42, MNP, or non-error correction (same as \N3). |
| \N7 | V.42, MNP, or non-error correction (same as \N3). |
\Qn - Flow Control Selection
| \Q0 | Disables flow control (same as &K0). |
| \Q1 | XON/XOFF software flow control (same as &K4). |
| \Q2 | CTS-only flow control. Not supported. |
| \Q3 | RTS/CTS hardware flow control (same as &K3). Default. |
\Tn - Inactivity Timer
n = 0, 1–255
Sets the time (in minutes) the modem waits after the last character is sent or received before disconnecting. A value of zero disables the timer. Applies only in buffer mode.
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NOTE: You can also set the inactivity timer by changing the value of S30. |
\Vn - Protocol Result Code
| \V0 | Disables the appending of the protocol result code to the DCE speed. Default. |
| \V1 | Enables the appending of the protocol result code to the DCE speed. |
| \V2 | Same as \V1. |
\Xn - XON/XOFF Pass-Through
| \X0 | Modem responds to and discards XON/XOFF characters. Default. |
| \X1 | Modem responds to and passes XON/XOFF characters. |
| -C0 | Disables V.25 data calling tone to deny remote data/fax/voice discrimination. Default. |
| -C1 | Enables V.25 data calling tone to allow remote data/fax/voice discrimination. |
%An - Adaptive Answer Result Code Enable
The %An command controls whether the "DATA" and "FAX" result codes will be sent by the modem. The modem must be in fax mode for this command to work. Also, the modem must be set to +FAA=1, which enables the modem to distinguish between a fax and a data call. When these commands are enabled, the modem sends "DATA" to the computer when it detects data tones, and "FAX" when it detects fax tones. These strings are used by some servers to select the appropriate communication program.
| %A0 | Disables adaptive answer result codes. Default. |
| %A1 | Enables adaptive answer result codes. |
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NOTE: For descriptions of the +FAA= and other fax commands, see the Multi-Tech Fax Class 2 Developer's Kit. |
%B - View Numbers in Blacklist
If blacklisting is in effect, AT%B displays the numbers for which the last call attempted in the previous two hours failed. In countries that do not require blacklisting, the ERROR result code appears.
%Cn - Data Compression Control
| %C0 | Disables V.42bis/MNP 5 data compression. |
| %C1 | Enables V.42bis/MNP 5 data compression. Default. |
%DCn - AT Command Control
| %DC0 | The modem responds to AT commands. Default. |
| %DC1 | The modem ignores AT commands. |
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NOTE: The modem will respond to AT%DC for 10 seconds after power-up. |
%En - Fallback and Fall Forward Control
| %E0 | Disables fallback and fall forward. |
| %E1 | Enables fallback, disables fall forward. |
| %E2 | Enables fallback and fall forward. Default. |
| $D0 | Disables DTR dialing. Default. |
| $D1 | Dials the number in memory location 0 when DTR goes high. |
$EBn - Asynchronous Word Length
| $EB0 | Enables 10-bit mode. Default. |
| $EB1 | Enables 11-bit mode. |
+ES=n - Enable Synchronous Buffered Mode
| +ES=6 | Allows an H.324 video application direct access to the synchronous data channel. On underflow, the modem sends HDLC flag idle (0x7E) to the remote modem. This special error control mode is overridden by any of the following commands: &F, &M, &Q, or \N. |
| +ES=? | Shows the allowed value. |
| +ES? | Shows the current value. |
#CBAn - Callback Attempts
n = 1–255
Default: 4
Sets the number of callback attempts allowed after passwords have been exchanged between modems.
#CBDn - Callback Delay
n = 0–255
Default: 15
Sets the length of time (in seconds) that the modem waits before calling back the remote modem.
#CBF? - Callback Failed Attempts Display
Requests the number of failed callback passwords since reset or power-up. This number can be stored to nonvolatile memory using the &W command.
#CBFR - Callback Failed Attempts Reset
Resets the number of failed callback passwords to 0. This does not reset the number stored in nonvolatile memory.
#CBIn - Local Callback Inactivity Timer
n = 1–255
Default: 20
Sets the time (in minutes) that the modem waits for a command before requiring the user to enter the setup password again.
#CBNy=x - Store Callback Password
y = 0–29
x = password
Sets the callback security password for the y memory location. The password must have 6 to 10 characters, and cannot include the + or - characters.
#CBPn - Callback Parity
Sets parity for the callback security messages. The parity of the messages should match the parity of the computer the modem is attached to.
| #CBP0 | No parity. Default. |
| #CBP1 | Odd parity. |
| #CBP2 | Even parity. |
#CBRy - Callback Security Reset
y = 0–29
Clears the password and phone number in the y memory location.
#CBSn - Callback Enable/Disable
Enables or disables callback security options. When callback security is enabled, phone number memory locations 0–4, used for quick dialing and DTR dialing, become unavailable and are replaced by callback security memory locations 0–29. The phone number memory locations and their contents are restored when callback security is disabled.
| #CBS0 | Disables callback security. Default. |
| #CBS1 | Enables local and remote callback security. |
| #CBS2 | Enables remote callback security only. |
| #CBS3 | Disables callback security until local hangup or reset. |
#Pn - Set 11-bit Parity
Sets 11-bit parity.
| #P0 | No parity. |
| #P1 | Odd parity. |
| #P2 | Even parity. Default. |
#Sx - Enter Setup Password
x = password (1–8 characters, case sensitive)
Default: MTSMODEM
Enters the remote configuration setup password.
#S=x - Store Setup Password
x = password (1–8 characters, case sensitive)
Default: MTSMODEM
Stores a new remote configuration setup password.
+++AT<CR> - Escape Sequence
Puts the modem in command mode (and optionally issues a command) while remaining online. Type +++AT and up to ten command characters, then press ENTER. Used mostly to issue the hang-up command: +++ATH<CR>.
%%%AT<CR> - Remote Configuration Escape Sequence
Initiates remote configuration mode while online with remote modem. The remote configuration escape character (%) is defined in register S13.
Fax commands resemble AT commands, but are more complicated to use. Because of this, we recommend that you use a fax program to send and receive faxes rather than attempting to control the modem directly. Developers who need to know the fax commands for the MT5634ZBA can download the following guides from the Multi-Tech FTP site:
MT56XX Fax Class 1 Developer's Guide
Fax Class 2 Developer's Kit