Below are modem commands that can be used with AT (Hayes) compatible modems. All commands are used with the ‘AT’ prefix. For example, to manually set the speaker volume to medium, the ATL2 command would be entered in a communications program (such as Terminal or Hyperterminal).

NOTE: These are general modem commands. Certain commands may not work with all modems. Consult the documentation for your modem if you experience difficulties, or contact your modem manufacturer’s technical support department.

AT Command Reference
%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
)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 Online Data Mode
P : Set Pulse Dial Default
Qn : Result Code On/Off
Sn : Select a Specific S Register
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
Sn=x : Write an S Register Value
&Zn=x : Store Phone Number

&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.
&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.

&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.
E0 : Inhibits the command echo.

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.
V0 : Selects result codes in NUMERIC format.

V1 : Selects result codes in WORD format.

The following 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 speaker during call establishment, but off after 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.

Additional information may be found at the Hayes Web site and the US Robotics Web site. Also, your modem manufacturer may have additional information about AT commands that your modem supports.