The following is a rundown of the Hayes "AT" Command set.
AT -- ATtention AT is not strictly a command; rather, it signals the modem that a command will follow -- in essence, it says "ATtention". This two-letter signal must appear at the beginning of a command line.
A/ -- Repeat This command is not preceded by AT and need not be followed by a carriage return. It instructs the modem to repeat the action or actions of the previous command line.
A -- Answer This command instructs the modem to begin the answer sequence immediately. It can be used to switch from a voice call to a data call.
B -- Bell/CCITT This command instructs the modem to conform to one of several standard modem operating protocols when transmitting at 1200 bits per second. (At any other transmission speed, the speed selects the protocol.) B0 causes the modem to operate in CCITT V.22 mode. B1 causes the modem to operate in Bell 212A mode (default).
D -- Dial This command instructs the modem to go off-hook and dial the numbers that follow it, then originate a data call. The Dial command can be modified with several symbols and letters, as follows: P instructs the modem to use pulse dialing. R causes the modem to establish a call in Answer Mode, rather than in Originate Mode. This command is used to dial a call to a modem that can only originate a call. T instructs the modem to use tone dialing. W directs the modem to wait until a dialtone is detected. If a dialtone is not detected within a specified length of time, the modem hangs up and displays "NO DIALTONE". 0-9 are the digits of a telephone number to be dialed. Can also transmit the * and # symbols with tone dialing. , (comma) directs the modem to pause for a specified length of time before processing the next symbol in the command. The default pause is 2 seconds. (The length of the pause is changed by using the S8 command eg ATS8=2). ; (semicolon) instructs the modem to return to command mode at the end of the command line, instead of originating a data call. The semicolon can be entered anywhere in the command line, and the modem's speaker stays on until you instruct the modem to hang up (AT H). ! Causes a hook flash of 1/2 second. @ Instructs the modem to wait a specified time (default 30 seconds) for one or more rings followed by 5 seconds of silence before processing the next symbol. / causes a pause of 1/8 second in the dialing sequence.
E -- Echo E0 disables echoing of commands on the screen. E1 causes commands to be echoed on the screen (default)
F -- Duplex F0 selects half-duplex F1 selects full-duplex (default)
H -- Hook Switch Control H0 instructs the modem to drop the line (default). H1 instructs the modem to seize the line.
I -- Inquire I0 produces the modem's identification code. I1 produces the checksum of the ROM. I2 causes modem to display its current transmission speed, number of data bits, and parity in the following format. SSSS Transmission speed: 0300 , 1200 , or 2400 (default). L Data bits: 7 (default) or 8 P Parity: (E)ven (default), (O)dd, (N)one, (M)ark, or (S)pace.
L -- Loudness (of speaker) L0 sets modem speaker at low volume L1 sets volume to the same as L0 L2 sets speaker at medium volume (default) L3 sets speaker at high volume.
M -- Monitor (via speaker) M0 keeps speaker off at all times M1 keeps speaker on until modem connection is established, then turns it off; speaker turns back on if connection is lost -- used for data-to-voice switching. (default) M2 Keeps speaker on at all times M3 Keeps speaker on except when the modem detects a remote carrier or is dialing.
O -- On-line This command switches the modem from Command Mode to On-Line Mode and instructs the modem to go off-hook and originate without dialing. You would use the On-Line command when you want to switch from voice to data, with your modem taking control (by originating)
Q -- Quiet Q0 causes responses to commands to be displayed (default) Q1 requests no responses.
S -- S-Registers The Modem uses a portion of its memory to store operating information, such as the length of time it will wait for a dialtone and the number of rings before it will answer. There are 28 of these small partitions, called S-Registers; they are labeled S0 through S27. S? displays the values stored in the specidied S-Register. It takes the form Sn? in which n is a number from 0 to 27. The command AT? will display the value stored in the S-Register most recently accessed. S= sets the value in the specified S-Register. It takes the form Sn=r in which n is the number of the register and r is the value to be set. (Examples: S0=3;S10=90) The command AT=r changes the value of the S-Register most recently accessed to r.
V -- Verbose Response V0 instructs the modem to display responses in their numerical form. V1 instructs the modem to display responses in verbal form (default)
X -- Response Sets The modem has five levels of on-screen responses. The X command specifies the level to be displayed by the modem. X0 specifies the minimum set of responses. X1 like X0 but the modem does not wait for dialtone before dialing. X2 like X1 but adds wait for dialtone before dialing. X3 like X1 but adds call progress messages and tone detection; the modem does not wait for dialtone before dialing. X4 like X1 but adds call progress messages, tone detection and wait for dialtone (default)
Y -- Long Space Disconnect This command specifies whether the modem will disconnect and hang up after any break of more than 1.6 seconds. Also, when this command is in effect, the modem will transmit a 4-second space before dropping the line. Y0 turns off long space disconnect (default) Y1 turns on long space disconnect
Z -- Reset This command resets all operating conditions and S-Registers to their default settings. It responds with OK on the screen before executing the reset; you should wait 1/2 seconds before typing any additional command.
&D - DTR Options This command controls the effect of dropping Data Terminal Ready (DTR) during a data call &D0 causes the modem to ignore DTR &D1 causes the modem to revert back to Command Mode on the ON-to-OFF transition of DTR &D2 causes the modem to go back on-hook and disable auto-answer on the ON-to_OFF transition of DTR. Auto-Answer will be re-enabled (if it was disabled) when DTR is turned back on. (default) &D3 causes the modem to reset on the ON-to-OFF transition of DTR
&G - Guard Tones This command selects the frequency of guard tones, which are used in some telephone systems abroad but are not used in the U.S. &G0 selects none (default) &G1 selects 550 Hz. &G2 selects 1800 Hz.
&L - Line This command chooses between standard dial-up telephone lines and leased lines. &L0 selects dial-up line (default) &L1 selects leased line
&P - Pulse Ratio This command selects the off-hook (make) to on-hook (break) interval, called the make-break ratio, for pulse dialing. It also controls adaptive dialing, which means that when tone dialing is in effect the modem checks for a dialtone after dialing the first digit; if the dialtone persists, the modem changes to pulse dialing and resends the first digit. &P0 selects a ratio of 39:61 (United States) without adaptive dialing (default) &P1 selects 33:67 (United Kingdom, Hong Kong) without adaptive dialing &P2 selects U.S. timing with adaptive dialing. &P3 selects UK timimg with adaptive dialing.
&T - Test This command selects the modems test and diagnostic features and will change with individual types of modems. Example: &T1 begins a local Analog Loopback test. &T3 Local Digital Loopback test. &T4 accept a request for from a remote modem for a RDL test ** and so on **
+++ - Escape This command, like the Repeat command, is not preceded by AT or followed by <return>. You must pause at least 1 second after typing any other character before typing the Escape sequence and at least 1 second after typing it before typing anything else. The Escape command switches the modem from On-Line Mode to Command Mode without breaking the connection. The modem responds with OK. You can return to On-Line Mode with the AT O command. The Escape can also be used to terminate the self test mode.