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Modem AT Command Codes

Thise are the standard "Hayes" compatible Modem AT commands. Some commands will vary between manufactures, so if your modem manufacture has their own AT Command code list you should use that insead.
AT Attention Gets the modems attention; this prefix must be included in all commands unless otherwise noted.
+++ Escape Sequence Switches the modem from data to command state, which usually disconnects modem.; this command is not proceeded by AT. Most modem have a "guard time" of 1 second in which no additional data should be sent to the modem before or after the escape code is sent, or it will be ignored.
A Answer Instructs the modem to attempt to answer a call.
A/ Again Re-executes the last modem executed command; this is not proceeded by AT.
Bn Select Protocol Sets the operation standard. B0=CCITT, B1=Bell
Cn Transmittion Carrier Turns the modem transmit carrier signal on and off. C0=turn off the modem transmit carrier signal during normal operation; C1=Turn on modem transmit carrier signal during normal operation.
Dn Dial Dials the number, n; T =- Touch-Tone dialing; P = Pulse dialing; a comma character will pause 1 second; @ = Wait for 5 seconds of silence; R = Dial an originate-only modem;
"DS=n" = Dial one of four stored telephone numbers; : = Return to command mode after dialing; ! = Go on hook for 1/2 second.
En Echo Turns the command echo feature on/off so that your commands either are displayed or are not displayed on the screen. C0=off, C1=on.
Hn Hook Causes the modem to hang up (place on hook) or pick up (take poff hook)when in command mode H0=hang up, H1=pick up.
In ID Identifies the modem code and the status of the ROM 0=display 3-digit product ID code (preset to 248); 1=display checksum; 2=display checksum and display OK or ERROR.
Ln Loudness Sets the internal speaker volume 0,1=lowest, 2=medium, 3=highest.
Mn Speaker Mode Determines when the speaker is on and off; 0=always off; 1=on during call and off when receiving data carrier; 2=always on; 3=off when receiving carrier and during dialing but not when answering.
On On-Line Switches the modem from the command state to the on-line state; 0=returns the modem to the on-line state when a connection is still open, 1=returns the modem to the on-line state and initiates a V.22 bis retrain sequence.
Qn Result Codes Displays or suppresses (quiets) result codes 0=displays codes. Default, Q1=suppresses codes
Sr? S-Register Read Read and display registerr
Sr=n S-Register Write Set register r to value n. See S Register Command Codes
Vn Result Format Displays result codes in short form (numbers) or long form (test); V0=Send numeric responses; V1=send word responses.
Xn Result Code & tone detect Determines which result codes will be displayed following modem operations; 0=Basic response set, blind dialing; X1=Extended response set, blind dialing; X2=Extended response set, dial tone detection; X3=Extended response set, blind dialing, and busy signal detection; X4=Extended response set, dial tone, and busy signal detection.
Yn Long-space Disconnect Enables or disables the long-space disconnec.t Y0=disable, Y1=enable.
Zn Reset or Restore Resets the modem or restores a user profile; Z=Reset, Z0=restore user profile 0; Z1=restore user profile 1.
&Cn DCD Option Controls the Data carrier Detect signal, leaving the DCD interchange circuit on at all times or turning it on only when a data carrier is detected; &C0=force DCD signal active, &C1=DCD signal indicates true state of remote carrier signal.
&Dn DTR Responce Controls data terminal ready (DTR) transition 0=Ignore DTR signal; 1=Return to command mode when after losing DTR; 2=Hang up, turn off auto answer, and return to command mode after losing DTR; 3=Reset after losing DTR.
&Fn Factory Defaults Returns the configuration to the factory settings; &F=Fetch default configuration 0 ; &F1=Recall factory default configuration 1 (only works with some modems.
&Gn Guard Tone Selects the guard tone (not used on calls within the U.S.); 0=Disable guard tone; 1=set guard tone on answering modem to 550 Hz; 2=Set guard tone to 1800 Hz.
&Mn Communication Mode Sets operation; &M0=Sets asynchronous operation. &M1, &M2, &M3= sets Synchronous modes.
&Pn Pulse Dial Make/Break Selects the ratio of the make/break interval that the modem uses for pulse dialing; "make" refers to off-hook, "break" refers to on-hook; &P0=39/61 for U.S., &P1=33/67 for United kingdom.
&Sn DSR Option Select &S0=Force DSR signal active; &S1=DSR active according to the CCITT specification.
&Tn Test Option &T 0=End current test; &T1=Start local analog loop back test; &T2=Unknown; &T3=Start local digital loop back test &T4=Grant remote request for remote digital loop back test; &T5=Deny remote request for remote digital loop back test; &T6=Start remote digital loop back test; &T7=Start remote digital loop back test with self-test; &T8=Start local analog loop back test with self-test.
&V View Profile Displays the user profiles and stored numbers.
&Wn Write Profile Stores the current configuration as Profile 0 or 1 0=Profile 0, 1=Profile 1.
&Xn DTE Clock Source Selects the synchronous clock source; &X0=Internal Timing, . &X1=External Timing from local DTE, &X2=receive timing from remote carrier.
&Yn Active Profile Read Selects which user profile will be the default at power -on and reset; 0=Profile 0, 1=Profile 1.
&Z=x Phone number Write Stores telephone numbers x in location n (0-3) x=up to 32 characters. For pulse dialing, 0-9 and dial modifiers for touch dialing, 0-9, dialing modifiers, A-D, #, and *.


\An Selects the maximum MNP block; 0=64-character maximum MNP block; 1=128-character maximum MNP block; 2=192-character maximum MNP block; 3=256-character maximum MNP block.
\Bn - Sends a break command to a remote modem n=0-9 in 100 milliseconds.
\Cn - Specifies whether data is to be buffered or not; 0=Do not buffer data; 1=Buffer data for 3 seconds, until character are received, or until packet is detected.
D/n - Dials one of four stored telephone numbers.
DL - Redials the last telephone number dialed.
\Gn - Disables or enables DCE flow control.
\Jn - Turns off or turns on DTE baud adjustment; 0=Turn off DTE baud rate adjustment.
\K - Sets the break control.
\Nn - Selects connection; 0=Allows standard buffered connection only; 1=Allows direct connection only; 2= Allows reliable (MNP) connection only; 3=Allows auto reliable (MNP) connection.
\P - Stores telephone number.
\Qn - Selects flow control; 0=Turns off DTE flow control 1=XON/XOFF bi-directional software flow control; 2=CTS signal unidirectional software flow control; 4=XON/XOFF unidirectional flow control (V.42 only)
\S - Displays modem status.
\T - Inactivity timer.
\U - Accepts reliable link from standard link.
\Vn - Selects send or do not send for MNP responses.
\Xn - Sets standard XON/XOFF pass through flow control. This command works only when a standard buffered connection has been established and XON/XOFF flow control is being used. 0=Modem acts on XON/XOFF received from the local DTE, but does not pass XON/XOFF to the remote modem. 1=Modem acts on XON/XOFF received from the local DTE and passes XON/XOFF to the remote modem. This allows the local DTE to XON/XOFF the remote DTE through the established modem link.
\Y - Switches standard link to reliable link.
\Z - Ends the reliable connection and switches to the standard connection.
%A - Sets the auto-reliable fallback character.
%Cn - Disables or enables class 5 MNP operation; 0=Disable class 5 MNP operation 1=Enable Class 5 MNP operation.
%En - Disables or enables auto retain 0=Disable auto retain, 1=Enable auto retain.

Click here for listing of S-Registers


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