Editing Hayes AT command set (section)

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

{| class="wikitable"
|+ Basic Hayes Command Set
! Command
! Description
! Comments
|-
| '''A0''' or '''A'''
| Answer incoming call
| &nbsp;
|-
| '''A/'''
| Repeat last command
| Do not preface with '''AT''', do not follow with carriage return. Enter usually aborts.
|-
| '''D'''
| Dial
| Dial the following number and then handshake<br />
P – Pulse Dial<br />
T – Touch Tone Dial<br />
W – Wait for the second dial tone<br />
R – Reverse to answer-mode after dialing<br />
@ - Wait for up to 30 seconds for one or more ringbacks<br />
, - Pause for the time specified in register S8 (usually 2 seconds)<br />
<nowiki>;</nowiki> – Remain in command mode after dialing.<br />
<nowiki>!</nowiki> – Flash switch-hook (Hang up for a half second, as in transferring a call.)<br />
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 if the computer software does not support echo)
|-
| '''H0''' or '''H'''
| 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 is not 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 with speakers. Modems lacking speakers, or with physical volume controls, or ones whose sound output is piped through the sound card will not support this command.
| 0 turns off speaker, 1 to 3 are for increasing volumes.
|-
| '''M0''' or '''M'''
| Speaker Mute, completely silent during dialing
| '''M3''' is also common, but different on many brands
|-
| '''M1'''
|
| Speaker on until remote carrier detected (user will hear dialing and the modem handshake, but once a full connection is established the speaker is muted)
|-
| '''M2'''
|
| Speaker always on (data sounds are heard after <code>CONNECT</code>)
|-
| '''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. <code>OK</code>)
|-
| '''Q1'''
| Quiet Mode
| On – Result codes are suppressed, user does not see responses.
|-
| '''S''<code>n</code>'''''
| rowspan="3" | Select current register

Note that '''S''<code>n</code>''''', '''?''' and =''<code>r</code>'' are actually three separate commands, and can be given in separate '''AT''' commands.
| Select register ''n'' as the current register
|-
| '''S''<code>n</code>''?'''
| Select register ''n'' as the current register, and query its value. Using '''?''' on its own will query whichever register was most recently selected.
|-
| '''S''<code>n</code>''=''<code>r</code>'''''
| Select register ''n'' as the current register, and store ''r'' in it. Using '''=''<code>r</code>''''' 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. <code>CONNECT</code>, <code>BUSY</code>, <code>[[NO CARRIER]]</code> etc.)
|-
| '''X0''' or '''X'''
| Smartmodem
| Hayes Smartmodem 300 compatible result codes
|-
| '''X1'''
|
| Usually adds connection speed to basic result codes (e.g. <code>CONNECT 1200</code>)
|-
| '''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, and usually also physically power-cycles the modem (during which it is unresponsive). '''Z0''', '''Z1''' etc. are for multiple stored profiles. '''&amp;F''' is similar in that it returns to factory default settings on modems without NVRAM (non volatile memory), but it does not reset the modem
|}
Note: a command string is terminated with a CR (\r) character

Although not part of the command set, a [[tilde]] character '''~''' is commonly used in modem command sequences. The '''~''' causes many applications to pause sending the command stream to the device (usually for half a second), e.g. after a ''Reset''. The '''~''' is not sent to the modem.<ref>{{Cite web|url=http://www.chebucto.ns.ca/Help/Dialup/MoreModemCommands.shtml |title=More Modem Commands |publisher=Chebucto Community Net |access-date=2016-09-12}}</ref>