6. 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). ZTerm handles the dial command, but 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 “Hayes compatible” 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.
There are three places in ZTerm where you can enter a modem
command. In the Modem Preferences there are the initialization
and deinitialization strings. These two are to do any modem
configuration needed when ZTerm starts and quits. And in the
Connection settings for each service there is the PreDial init
string. This is to make any modem configuration changes needed
just for this service. In addition, you can manually type a modem
command in the terminal window. This is a good way to try out
modem commands or to do one-time changes.
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 “CONNECT” instead of just “1”).
ATZ - reset modem to default configuration.
ATS0=1 - set modem to auto answer after one ring. (That’s a zero after
the S).
ATS0=0 - turn off auto answer.