[Citilink Internet - Minneapolis MN, USA] The Hayes Command Set ------------------------------------------------------------------------ The Hayes Command Set The modem initialization string consists of a series of commands. It prepares the modem for communications, setting such features as dialing mode, waits, detection of the busy signal and many other settings. Newer modem communications programs reset the initializations string for you according to which menu options you select, which features you enable, etc. For many years Hayes modems have been the standard. As the field of modem manufactures has grown, most have adhered at least loosely to the Hayes standard. The following is a partial list of the Hayes command set. (called the AT commands). The Hayes Command Set can be divided into four groups: Basic Command Set A capital character followed by a digit. For example, M1. Extended Command Set An "&" (ampersand) and a capital character followed by a digit. This is an extension of the basic command set. For example, "&M1". Note that "M1" is different from "&M1". Proprietary Command Set Usually started by either a backslash ("\"), or a percent sign ("%"), these commands vary widely among modem manufacturers. For that reason, only a few of these commands are listed below. Register Commands Sr=n where "r" is the number of the register to be changed and "n" is the new value that is being assigned. A "register" is computerese for a specific physical location in memory. Modem have small amounts of memory onboard. This fourth set of commands is used to enter values in a particular register (memory location). The register will be storing a particular "variable" (alpha-numeric information) which is utilized by the modem and communication software. For example, S7=60 instructs your computer to "Set register #7 to the value 60." Note: Although most commands are defined by a letter-number combination (L0, L1, etc.), the use of a zero is optional. In this case, L0 is the same as a plain "L" - keep this in mind when reading the table below! Here are some of the most important characters that may appear in the modem initialization string. These characters normally should not be changed. AT tells the modem that modem commands follow. This must begin each line of commands. Z resets the modem to default state , (comma) makes your software pause for a second. You can use more than one , in a row. For example, ",,,," tells the software to pause four seconds. (The duration of the pause is governed by the setting of register S8. ^M sends the terminating Carriage Return character to the modem. This is a control code that most communication software translate as a "carriage return." ------------------------------------------------------------------------ The Basic Hayes Command Set - Alphabetical Command - Description - Comments A0 or A Answer incoming call A/ Repeat last command. (Don't preface with AT. Enter usually aborts.) B0 or B V32 Mode/CCITT ans Seq B1 Call negotiation Bell 212A Answer Seq B2 Verbose/Quiet On Answer Dial the following number and then handshake in originate mode. Dial Modifiers (These are common but most modems will have more.) P Pulse dial T Touch Tone dial D Dial W Wait for second dial tone , Pause for 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 or H On hook - hang up Hook status H1 Off hook - phone picked up (This command is very model specific. I0 usually returns a I0 or I Inquiry, Information, or number or code, while higher numbers Interrogation often provide much more useful information.) L0 or L Speaker Loudness Off or low volume L1 Low volume Modems with volume control L2 knobs will not have these Medium volume L3 options. Loud or high volume M0 or M (M3 is also common, but different on many brands) Speaker on until remote carrier M1 Speaker off detected (until the other modem is heard) M2 Speaker is always on (data sounds are heard after CONNECT) N0 or N Handshake only at speed in S37 Handshake Speed Handshake at highest speed larger N1 than S37 O0 or O (O0 see also X1 as dial tone detection may be active) Return Online O1 Return Online after an equalizer retrain sequence Q0 or Q Off - Displays result codes, user sees command responses (e.g. OK) Quiet mode Q1 On - Result codes are suppressed, user does not see responses Sn? Query the contents of S-register n Sn=r Store Store the value r in S-register n V0 or V Numeric result codes Verbal? English result codes (e.g. CONNECT, V1 BUSY, NO CARRIER etc.) X0 or X Hayes Smartmodem 300 compatible result codes Usually adds connection speed to X1 basic result codes (e.g. CONNECT 1200) Smartmodem Usually adds dial tone detection X2 (preventing blind dial and sometimes ATO) X3 Usually adds busy signal detection X4 Usually adds both busy signal and dial tone detection Reset modem to stored configuration (Z0, Z1 etc. for multiple profiles) Z0 or Z Reset (Same as &F (factory default) on modems with out NVRAM (non volatile memory) ------------------------------------------------------------------------ The Extended Hayes Command Set (Ampersand Commands ) Command - Description - Comments &B0 or &B Disable auto retrain function &B1 Enable auto retrain function Retrain Parameters Enable auto retrain, but disconnect if &B2 no line improvement over period dictated by S7 &C0 or &C signal always on Carrier detect Indicates remote carrier (usual &C1 preferred default) &D0 or &D Signal ignored (See your manual on this one!) &D1 If DTR goes from On to Off the modem goes into command mode (some modems) Data Terminal Ready (DTR) &D2 Some modems hang upon DTR On to Off transition. (Usual prefered default) &D3 Hang up, reset modem and return to command mode upon DTR Generic Hayes-compatible defaults. This is usually a good thing to use in your init string, since the &F1-&F3 settings can vary among modems, and they may actually be the cause of connection problems. (Since you never know exactly what Brand X's &F2 really &F0 or &F changes. On the other hand, it pays to try out the other options below; many people's Factory defaults problems can be solved by replacing a complicated init string with a simple &F2 or the like. However, if you're building an init string, it's best to start with a simple &F, and not use the "customized" form of defaults. &F1 Factory defaults tailored to an IBM-PC compatible user &F2 Factory defaults for a Mac w/software handshaking &F3 Factory defaults for a Mac w/hardware handshaking &G0 or &G Guard tones Disable guard tones &K0 or &K Disable local flow control &K1 Enable RTS/CTS hardware local flow control Enable XON/XOFF software local flow &K2 Local flow control control &K3 Enable RTS/CTS hardware local flow control &K4 Enable XON/XOFF software local flow control &L0 or &L Dial mode Select dial-up mode &M0 or &M Error Control mode Select asynchronous non-EC mode (same as &Q0) &P0 or &P U.S./Canada pulse dialing 39% make/ 61% break ratio Pulse dialing ratio &P1 U.K./Hong Kong pulse dialing 33% make/ 67% break ratio &Q0 or &Q Asynchronous non-EC more. No data buffering. ASB disabled. &Q5 Select V.42 EC operation (requires flow control) Error Control mode Asynchronous mode with ASB (requires &Q6 flow control) &Q8 Select alternate EC protocol (MNP) &Q9 Conditional data compression: V.42bis = yes, MNP5 = no. &S0 or &S Always on (default) DSR Action Select Follows EIA specification (Active &S1 following carrier tone, and until carrier is lost.) &T0 or &T Self test Model specific self tests on some modems &U0 or &U Enable V.32 TCM Trellis code modulation &U1 Disable V.32 TCM &V0 or &V View active (And often stored) configuration profile settings (or ATI4) In NVRAM (&W0, &W1 etc. for multiple &W0 or &W Store profile profiles) Some settings cannot be stored. These often don't show on &V or ATI4 &Y0 or &Y Select Configuration Load profile 0 (default) &Y1 Loaded at power-up Load profile 1 &Zn=x Soft reset and Load Note: All items after the &Z on the Stored profile #n command line are ignored ------------------------------------------------------------------------ Backslash & Percent Commands: Command - Description - Comments \A0 or \A 64 character maximum \A1 Character maximum MNP block 128 character maximum \A2 size 192 character maximum \A3 256 character maximum %C0 or %C Disabled %C1 Data Compression MNP5 Enabled %C2 Enable/Disable V.42bis (BTLZ) Enabled %C3 MNP5 & V.42bis (BTLZ) Enabled %D0 or %D 512 BLTZ dictionary size %D1 1024 BLTZ dictionary size Data compression %D2 2048 BLTZ dictionary size %D3 4096 BLTZ dictionary size %E0 or %E ESCAPE DISABLED %E1 +++AT method (default) %E2 AT method Escape method %E3 BOTH methods enabled %E4 Disable "OK" to +++ %E5 Enable "OK" to +++ \J0 or \J Disabled DTE Auto Rate Adjustment DTE rate is adjusted to match J1 carrier rate. \N0 or \N Normal connection (see below for definitions) \N1 Direction connection \N2 MNP Auto-reliable connection \N3 Auto-reliable connection V.42bis reliable link with phase \N4 Connection type detection \N5 V.42bis auto-reliable link with phase detection \N6 V.42 reliable link with phase detection \N7 V.42 auto-reliable link with phase detection Note: A direct connection is a simple straight-though connection without any error correction or data compression. In this case, the computer-to-modem and modem-to-modem speeds must be identical. A normal connection uses flow control (either software or hardware) to buffer the data being sent or received, so that the modem can transmit data at a different rate than the computer is actually sending or receiving it. For example, a computer may send actual data at 57kbps, but using compression, the modem only actually sends 28.8kbps. This is the mode use by most modems. A reliable connection is a type of normal connection; if, for some reason, data compression or error correction cannot be established or maintained, the connection will hang up. (In essence, such a modem ensures that all connections are reliable, for it will hang up if the connection isn't.) Likewise, an auto-reliable connection is virtually the same, except that the modem will try to renegotiate the connection in order to establish a reliable connection. Again, this is the mode that most modems use. ------------------------------------------------------------------------ S-Registers: Register Range Default Function S0 0-255 rings 1-2 Answer on ring number Don't answer if 0 S1 0-255 rings 0 If S0>0 this register counts incoming rings S2 0-127 ASCII 43 + Escape to command mode character S2 >127 no ESC S3 0-127 ASCII 13 CR Carriage return character S4 0-127 ASCII 10 LF Line feed character S5 0-32,127 ASCII 8 BS Backspace character S6 2-255 seconds 2 Dial tone wait time (blind dialing, see Xn) S7 1-255 seconds 30-60 Wait time for remote carrier S8 0-255 seconds 2 Comma pause time used in dialing S9 1-255 1/10 sec. 6 Carrier detect time required for recognition S10 1-255 1/10 sec. 7-14 Time between loss of carrier and hangup S11 50-255 millisec. 70-95 Duration and spacing of tones when tone dialing Guard time for pause S12 0-255 1/50 sec. 50 around +++ command sequence Fallback options when error correction link fails: 0 - Disconnect 1 - Establish Direct connection 3 - Establish Normal connection S36 4 - Establish a MNP 7 Negotiation Failure connection if possible, else Treatment Disconnect 5 - Establish a MNP connection if possible, else Direct connection 7 - Establish a MNP connection if possible, else Normal connection 1 = 300 bps 5 = 1200 bps 6 = 2400 bps 7 = 1200/75 bps (v.23 mode) S37 8 = 4800 bps 0 Negotiation Speed 9 = 9600 bps (Initial handshake) 10 = 12000 bps 11 = 14400 bps 12 = 7200 bps Many modems have dozens, even hundreds, of S registers, but only the first dozen or so are fairly standard. They are changed with a command like ATSn=N, and examined with ATSn? (e.g. "AT S10=70 S1?" would tell the modem not to hang up for seven seconds should it not hear the answering modem, and return the number of times the phone last rang.) ------------------------------------------------------------------------ { Table of Contents | Section Index | Glossary of Terms | Search the FAQ | Help Me! } ------------------------------------------------------------------------ Please send comments about the FAQ to Karl Erickson (kae@citilink.com) Copyright © 1995-1997 / Last Update / Request Info from Citilink / The Wabbit Hole