Hayes Command Set - The Basic Hayes Command Set

The Basic Hayes Command Set

The following commands are understood by virtually all modems supporting an AT command set, whether old or new.

Command Description Comments
A0 or A Answer incoming call
A/ Repeat last command Don't preface with AT, don't follow with carriage return. Enter usually aborts.
D Dial

Dial the following number and then handshake

P - Pulse Dial
T - Touch Tone Dial
W - Wait for the second dial tone
R - Reverse to answer-mode after dialing
@ - Wait for up to 30 seconds for one or more ringbacks
, - Pause for the time specified in register S8 (usually 2 seconds)
; - Remain in command mode after dialing.
! - Flash switch-hook (Hang up for a half second, as in transferring a call.)
L - Dial last number

E0 or E No Echo Will not echo commands to the computer
E1 Echo Will echo commands to the computer (so one can see what one types)
H0 Hook Status On hook. Hangs up the phone, ending any call in progress.
H1 Hook status Off hook. Picks up the phone line (typically you'll hear a dialtone)
I0 to I9 Inquiry, Information, or Interrogation This command returns information about the model, such as its firmware or brand name. Each number (0 to 9, and sometimes 10 and above) returns one line of modem-specific information, or the word ERROR if the line isn't defined. Today, Windows uses this for Plug-and-play detection of specific modem types.
L0 or Ln (n=1 to 3) Speaker Loudness. Supported only by some modems, usually external ones. Modems lacking speakers, or with physical volume controls, or ones whose sound output is piped through the sound card will not support this command. Off or low volume
M0 or M Speaker off, completely silent during dialing M3 is also common, but different on many brands
M1 Speaker on until remote carrier detected (i.e. until the other modem is heard)
M2 Speaker always on (data sounds are heard after CONNECT)
O Return Online Returns the modem back to the normal connected state after being interrupted by the "+++" escape code.
Q0 or Q Quiet Mode Off - Displays result codes, user sees command responses (e.g. OK)
Q1 Quiet Mode On - Result codes are suppressed, user does not see responses.
Sn Select current register

Note that Sn, ? and =r are actually three separate commands, and can be given in separate AT commands.

Select register n as the current register
Sn? Select register n as the current register, and query its value. Using ? on its own will query whichever register was most recently selected.
Sn=r Select register n as the current register, and store r in it. Using =r on its own will store into whichever register was most recently selected.
V0 or V Verbose Numeric result codes
V1 English result codes (e.g. CONNECT, BUSY, NO CARRIER etc.)
X0 or X Smartmodem Hayes Smartmodem 300 compatible result codes
X1 Usually adds connection speed to basic result codes (e.g. CONNECT 1200)
X2 Usually adds dial tone detection (preventing blind dial, and sometimes preventing ATO)
X3 Usually adds busy signal detection.
X4 Usually adds both busy signal and dial tone detection
Z0 or Z Reset Reset modem to stored configuration. Use Z0, Z1etc. for multiple profiles. This is the same as &F for factory default on modems without NVRAM (non volatile memory)

Note: a command string is terminated with a CR (\r) character

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