Hayes

Optima 144 PCMCIA

AT&FW2&C1&D2&Q9S7=120 OK ATS10=30S30=15S38=2S95=3S108=2 OK
W - connect response form.
&C - DCD operation. Default - forced on :-/. Probably for Macintosh.
&D - DTR off action. Default - ignore. To reset modem use &D3.
&Q - data format and link negotiation mode.
S30 - inactivity timeout (minutes).
S38 - forced disconnect timer (seconds).
S95 - custom connect response form.
S108 - something special (can't remember).

This modem is based on the AT&T chipset.

AT-command set

This concept generally means any commands which are prepended with AT-prefix. But really the complete command set depends on firmware. There are some common command sets that are called

Basic command set

Basic command set contains of some control commands, such as ATA, ATD, ATH..., and options, which are described below:
A - manually answer incoming call.
B - modulation type at V.22 (1200 bps). 0 - ITU-T, 1 - Bell 212A. In fact it is obsoleted.
D - dial a number. With modifiers.
E - command echo (0 - off).
H - Hook control (0 - on).
I - product information (0-9, usually 0-6).
L - speaker volume (0 - minimal/off).
M - speaker control (0 - off).
O - return on-line (with options).
P - pulse dialing by default.
Q - response control.
S - register control (see below).
T - tone dialing by default.
V - verbose responses (0 - off).
X - result code options.
Y - long space disconnect (0 - off).
Z - reload profile(s).
If the letter is optionally followed by digit, the letter without digit is equal to that one followed by zero (0).

Any modem has a set of control registers, so called S-registers, which can be set as ATSn=value . To read the value of register you should enter ATSn?.

Extended command set

All the extended commands are the letters prepended with the 'and' sign (&) and optionally followed by digits. They are:
&B - baud adjust control (1 - fixed DTE speed).
&C - DCD operation mode (1 - tracks carrier).
&D - DTR off action (2 - disconnect, 3 - modem reset).
&F - recall factory defaults.
&G - guard tone control (0 - off).
&J - line option control (mostly obsoleted and unused).
&L - line control (0 - dial-up, 1 - leased).
&M - data format (needed 0 except some cases).
&P - pulse dialing make/break ratio option.
&R - RTS control option.
&S - DSR control option.
&T - test commands.
&V - display active/stored profiles.
&W - write current profile to NVRAM.
&X - synchronization source (in synchronous mode only).
&Z - stored telephone numbers processing.
The values signed in parenthesises are preferable for an usual dial-up connection.

Many modem manufacturers support both basic and extended command sets, others support extended set partially or don't support at all.

MNP command set

The MNP commands are usually prepended with the 'per cent' sign (%) or backslash (\) and divided to "options" and "commands". The second category must be entered on-line. The quick list of "option" commands is followed:
\A - maximum MNP block size.
%A - MNP drop character.
\C - MNP buffering option (1 - with buffering).
%C - data compression option. Used to enable/disable MNP5 and/or V.42bis data compression protocols.
\G - modem flow control (DCE-DCE). It probably would be better to set this option equal 1, but much safer to keep 0.
%G - fallback/fallforward control. Sometimes %E is used instead.
\J - DTE baud adjustment control. When this command exist, &B is absent or has another meaning.
\K - break handling (3 - expedited, non-destructive. 5 - queued).
\L - MNP mode (block/stream). This option is mostly obsoleted.
\N - asynchronous connection options (4 - auto V.42/MNP, 5 - reliable). This option as \K is replaced often with some other command.
\Q - modem-terminal (DCE-DTE) flow control (3 - RTS/CTS). As previous, it is replaced often.
\T - inactivity timeout (in minutes). When no data is transmitted during the desired interval, modem disconnects. If 0 is set, no timeout is controlled.
\V - extended responses option (0 - off).
\X - Xon/Xoff processing option (0 - preferable).
The quick list of on-line commands is followed:
\B - send break to remote.
\O - request reliable connection.
\U - grant request for reliable connection.
\Y - switch to the reliable connection (analog of \O for originate mode and \U for answer).
\Z - switch to the normal mode.
There are also some so called V.42 commands:
-C - enable calling tone (0 - off).
-J - enable V.42 auto-detection phase (1 - on).
"H - V.42bis option (3 - in both sides).
"O - V.42bis dictionary size (6-250, >64 is preferable).
All these commands are supported partially in most known modems but rarely completely implemented.