Modem Commands

A modem is controlled by sending it commands.  There are commands to configure a modem and commands to attempt a connection (the dial command). You may have to learn about some commands if you need to do any special configuration of your modem.  This section will explain some of the most common commands used by ÒHayes compatibleÓ modems.  Advanced modems will have additional commands which are not described here and in many cases will be unique to that brand of modem.  You will need to consult your modem manual for all of its commands and settings.  Some modems have a command that will print a summary of its commands.  On US Robotics modems, the commands AT$, AT&$, ATD$ and ATS$ will give a help summary on a portion of the modem commands.

All modem commands start with AT, which is sometimes referred to as modem attention.  You could put several modem commands together on one line.  In this case, the AT would only be used once, at the beginning of the line.  A command is processed by the modem when it receives a RETURN.

Here are some of the more common modem commands:

ATA - answer an incoming call and attempt to connect.
ATDT 5551212 - dial the number using touch tones.
ATDP 5551212 - dial the number using pulse dialing.
ATE1 - turn on the echoing of modem commands.
ATH0 - hang up (go on hook).
ATM0 - speaker always off.
ATM1 - speaker on while dialing until connection established.
ATV1 - verbal result codes (sends ÒCONNECTÓ instead of just Ò1Ó).
ATZ - reset modem to default configuration.
ATS0=1 - set modem to auto answer after one ring. (ThatÕs a zero after the S).
ATS0=0 - turn off auto answer.