The Extended Hayes Command Set

Ampersand Commands

Table B.2. The Extended Hayes Command Set

CommandDescriptionComments
&B0 or &BRetrain ParametersDisable auto retrain function
&B1Retrain ParametersEnable auto retrain function
&B2Retrain ParametersEnable auto retrain, but disconnect if no line improvement over the period dictated by S7
&C0 or &C1Carrier detectSignal always on
&C1Carrier detectIndicates remote carrier (usual preferred default)
&D0 or &DData Terminal Ready (DTR)Signal ignored (This is modem specific, you must see your manual for information on this one!)
&D1Data Terminal Ready (DTR)If DTR goes from On to Off the modem goes into command mode (Some modems only)
&D2Data Terminal Ready (DTR)Some modems hang up on DTR On to Off transition (This is the usual preferred default)
&D3Data Terminal Ready (DTR)Hang up, reset the modem, and return to command mode upon DTR
&F0 or &FFactory defaults

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 changes.)

On the other hand, it pays to try out the other options below; many people's 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.

&F1Factory DefaultsFactory Defaults tailored to an IBM PC compatible user
&F2Factory DefaultsFactory defaults for a Mac w/software handshaking
&F3Factory DefaultsFactory defaults for a Mac w/hardware handshaking
&G0 or &GGuard tonesDisable guard tones
&K0 or &KLocal flow controlDisable local flow control
&K1Local flow controlEnable RTS/CTS hardware local flow control
&K2Local flow controlEnable XON/XOFF software local flow control
&K3Local flow controlEnable RTS/CTS hardware local flow control
&K4Local flow controlEnable XON/XOFF software local flow control
&L0 or &LDial modeSelect dial-up mode
&M0 or &MError control modeSelect asynchronous non-EC mode (the same as &Q0)
&P0 or &PPulse dialing ratioU.S./Canada pulse dialing 39% make / 61% break ratio
&P1Pulse dialing ratioU.K./Hong Kong pulse dialing 33% make / 67% break ratio
&Q0 or &QError control modeAsynchronous non-EC more. No data buffering. ASB disabled.
&Q5Error control modeSelect V.42 EC operation (requires flow control)
&Q6Error control modeAsynchronous mode with ASB (requires flow control)
&Q8Error control modeSelect alternate EC protocol (MNP)
&Q9Error control modeConditional data compression: V.42bis = yes, MNP5 = no.
&S0 or &SDSR action selectAlways on (default)
&S1DSR action selectFollows EIA specification (Active following carrier tone, and until carrier is lost.)
&T0 or &TSelf testModel specific self test on some modems
&U0 or &UTrellis code modulationEnable V.32 TCM
&U1Trellis code modulationDisable V.32 TCM
&V0 or &V1View active(and often stored) configuration profile settings (or ATI4)
&W0 or &WStore profileIn NVRAM (&W0, &W1 etc. for multiple profiles) Some settings cannot be stored. These often don't show on &V or ATI4
&Y0 or &YSelect configuration loaded at power-upLoad profile 0 (default)
&Y1Select configuration loaded at power-upLoad profile 1
&Zn=xSoft reset and load stored profile number nNote that all items after the &Z on the command line are ignored