Sending Commands to a Modem
(Hayes Compatible)

Command Function
AT Attention - Needed before every other command (except A/ and the escape code). For Example: ATDT
A/ Repeat the last command (Don't use ATA/)
A Set to answer mode immediately, without waiting for ring
Bn Set Bell mode (1200 bps protocol compatibility - V.22 or Bell 212A)
Use n=0 CCITT V.22 with 2100Hz Answer Back Tone
Use n=1 Bell 212A with 2225Hz Answer Back Tone
Cn Carrier state: n=0 OFF, n=1 ON
Dn Use the following symbols in a dialing string:
Symbol What It Does
, Pauses - for 2 seconds normally
W Wait for a tone before dialing the remaining digits.
@ Wait for a "quiet answer" before continuing with a string.
! Flash (go on-hook for ½ second). Used to get a new dial tone.
; Return to beginning after dialing. Must be at the end of a dial string.
Digits and characters that can be used in a dialing string.
(Must be tone dialing for ABCD)
T To set up touch tone dialing.
P To set up pulse dialing.
R Reverse Mode - Used to put the modem in answer mode as soon as dialing is finished.
S=n Stored Number - Used to dial a stored number in some systems.
To Disable Call Waiting:  Use *70,,  before your digits to dial (most telecos).
DT Get Dial Tone
En Echo modem command (ON or OFF)
n=0 echo OFF (NO)
n=1 echo ON (YES)
Fn Full or Half Duplex operation
n=0, Half Duplex
n=1, Full Duplex
Hn Hook relay set to ON or OFF hook
n=0 on hook (disconnect or hang up)
n=1 off hook
In Request product code and ROM checksum / Return product ID/checksum
n=0, Returns product ID - The modem sends its own 3-digit product code
n=1, Performs checksum and returns it. Requests numeric checksum from firmware ROM
n=2, Performs checksum and returns the result code. Request OK or ERROR state from the ROM checksum
n=3, Returns ROM part number and revision level
Ln Loudness (volume of speaker)
n=0, low
n=1, low
n=2, medium (prefered)
n=3, high
Mn Mode of Speaker Control
n=0, Speaker always OFF
n=1, Speaker ON when phone is off-hook; OFF when Carrier Detected
n=2, Speaker always ON
n=3, Speaker ON after dialing until Carrier Detected. Speaker is turned OFF when carrier signal received
On On-line Mode Set
n=0, Online.
Qn n=0, codes are sent
n=1, codes are NOT sent
Sn? Reads the contents of status register Sn. Displays the value of S-register n.
Sn=x S-register command - Used to modify an S register in the modem. It assigns a value x to the status register n. An &F or Z command resets the register to default values.
Vn Sets result code format. Verbose mode for result codes.
n=0, use digits (numeric)
n=1, use words
Xn Xtended result code enabled and dialing mode set.
n=0, Basic (300bps). Dial tone and busy signal not recognized (blind dialing). Result codes 0-4 enabled.
n=1, extended(no dialtone or busy signals are detected). Result codes 0-5 and 100 enabled.
n=2, extended(detects dialtone but not busy signals). Result codes 0-6 and 10 enabled.
n=3, extended(no dialtone detect but detects busy signals). Result codes 0-5,7 and 10 enabled.
n=4, extended(detects both dialtones and busy signals)
Yn Long Space Disconnect Option
n=0, disabled
n=1, enabled; disconnects after receiving 1.6 sec break.
Z Resets registers to default values with configuration profile from non-volatile memory.
&Cn Data Carrier Detect(DCD) handling enabled.
n=0, DCD always on. Modem keeps DCD (RS-232 pin 8) always on.
n=1, DCD set by modem when remote carrier detected. DCD tracks data carrier detected by modem.
&Dn Data Terminal Ready(DTR) handling enabled. DTR ON/OFF time specified by S25.
n=0, modem ignores DTR line (RS-232 pin 20)
n=1, modem switches to asynch command mode when DTR goes off.
n=2 does n=1,DTR off does n=1 plus disables auto answer, switches modem off hook, and returns to asynch command state.
n=3, modem initializes when DTR goes off.
&F Resets S Registers and Commands to factory default setings from ROM config profile, as a powerup would do.
&Gn Guard tone selected (only for CCITT modes, not used in US.)
n=0, no guard tones
n=1, 550 Hz guard tone
n=2, 1800 Hz guard tone
&Jn selects telephone Jack
n=0, RJ-11/RJ-41S/RJ-45S
n=1, RJ-12/RJ-13
&Ln selects line, dialin or leased
n=0, dialin operation
n=1, leased-line
&Mn Mode selected for asynchronous/synchronous communication
n=0, asynchronous
n=1, synchronous mode 1 -async dialing, then switch to synchronous operation
n=2, synchronous mode 2 -stored number dialing
n=3, synchronous mode 3 -manual dialing
&Pn selects make/break pulse length for Pulse dialing
n=0, 39% make, 61% break(US and Canada standard)
n=1, 33% make, 67% break
&Qn Communications Mode Option
  Idle State On Line State
n=0 Normal Asynchronous
n=1 Normal Reserved
n=2 Dial when DTR=1
Hangup when DTR=0
n=3 Task/Data, DTR=0/1 Reserved
&Rn Request to Send/Clear to Send handling (sync mode only)
n=0, CTS (RS-232 pin 5) tracks RTS (pin4)
n=1, modem ignores RTS and turns CTS on when ready to receive synchronous data
&Sn Data Set Ready(DSR) handling. DSR ON indicates that the modem is connected to a communication channel and is ready.
n=0, DSR always ON. Modem forces DSR ON whenever modem is turned on
n=1, DSR (RS-232 pin 6) operates according to EIA specs. DSR turned ON at start of hand- shaking, off in test mode, idle state, or when carrier is lost
&Tn Test mode(not available in 300bps mode)
n=0, terminate any test in progress after last command on a line, and return to command mode. n=1, initiates local analog loopback test
n=3, initiates local digital loopback test
n=4, sets modem to perform remote digital loopback when requested by another modem
n=5, prohibits remote digital loopback
n=6, initiates remote digital loopback with another modem
n=7, initiates remote digital loopback with self-test
n=8, initiates local analog loopback with self-test
&V Display active configuration profiles for S Register settings, commands, and telephone numbers. Inputs from DTE are ignored while this information is being sent.
&Wn Write S registers and command config profile, last DTE speed, and parity to non-volatile RAM for poer up or hard reset.
n=0, store active profile in location 0
n=1, store active profile in location 1
&Xn Select the synchronous transmit clock source (sync mode only)
n=0, Internal clock, modem generates timing and sends through pin 15
n=1, modem's host computer generates timing and sends it to modem on pin 24, which modem routes to pin 15.
n=2, Receive clock, modem derives timing from incoming signal and supplies it to pin 15
&Yn Select a stored profile to survive a power outage for power up (in addition to &Y)
n=0, Select profile 0 on power up or hard reset
n=1, Select profile 1 on power up or hard reset See, the &Wn command for particular commands and S Registers stored. The selected &Y command survives a power outage.
&Zn Stores telephone number. n=string of digits compatible with Dn