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Chapter 3 - Software Configuration
3.8 Modem Basics
You control your modem by issuing AT commands, setting S-Registers, and setting DIP-Switches.
You can easily change the settings of your DIP-Switches, as they are located on the right side of
your modem’s chassis. Right now your modem is set up for the most typical user application, that is,
as a traditional modem set to make a dial-up call to a remote installation where the call is answered
automatically; therefore, you shouldn’t need to change the DIP-Switches. (If however, you know that
your application does not follow this profile, please refer to Chapter 9 for full details on DIP-Switch
settings.)
While you may operate your modem manually, it is more likely that you will use your data
communications software to either:
• enter “terminal” mode, where you can “speak most directly” to the modem by issuing AT
commands, or to
• launch a datacomm session through a set of modem configurations which you select and then
associate with a target telephone number. Once you have created, saved, and named this set of
information according to your connection needs and your datacomm software’s conventions, the
software then simplifies your dialing because you needn’t re-configure your modem, nor run the
risk of mistakenly keying-in incorrect information.
Either way, you need to understand that an AT command is the method by which your modem is
controlled, and must therefore prefix nearly all commands. AT stands for attention, and alerts the
modem that a command follows. You may enter these commands with either upper- or lowercase
characters. Entering AT automatically sets the modem’s serial baud rate to match your computer’s
and also sets the modem’s parity. It also clears the modem’s command buffer.
Once you’re in terminal mode, enter AT followed by <CR> to check whether your modem is
operational. If everything’s fine, your modem will respond OK. (Note: refer to Chapter 4 for additional
details on Dialing, Automatic Answering, Dial Back-Up and Automatic Leased Line Restoral.)
3.8.1 Simple Operations
You can dial a number by using the ATD command and the phone number of the modem with which
you wish to connect, e.g., ATD6127853500. Your modem will dial the number, and hear a
“scrambling” noise as the modem negotiates the kind of connection it can make, and once the
modems have settled on a common connection, you will receive a connect message on your
computer’s video display. As the modem dials and connects, you may notice changes across its front
LED panel: the OH (Off Hook) LED lights to let you know the modem is operating as if you had
picked up the handset to a phone. The CD (Carrier Detect) LED lights to let you know the modem
has detected a device it can connect to. A speed LED lights to let you know at which speed the
connection has been made.
To hang up a call, enter +++ATH<CR>. Your modem will return on hook, just as if you had returned a
phone’s handset to its cradle. Notice also that the OH, CD and speed LED’s are no longer lit. Your
video now displays OK, signifying that your modem is ready for your next command.
3.9 The Answer/Originate - Voice/Data Toggle Switch
Located on the front of the modem is a Voice/Data "toggle" switch with Originate/Answer capabilities.
This switch enables the modem to automatically dial a phone number stored in the N1 location of
memory whenever this switch is toggled. (Note that you must first enter AT$VD1&W0<CR>. This
command string enables Voice/Data dialing when the Voice/Data toggle switch is activated.)
If you are "Manually" dialing with an attached telephone device (and not with your keyboard), your
modem originates when toggled in that position (DOWN); and if you are "Manually" answering
(modem is not configured to automatically answer via S-Register S0 setup), the modem answers an
incoming call when toggled in that position (UP).