2400 BPS Internal Modem  (250-3025)      Commands      Faxback Doc. # 4921

Initializing Commands:

Using an Initialization String Instead of DIP Switches to Configure the
Modem:

Some older software packages have instructions for setting the modem's DIP
switches, because many 1200 bps modems used DIP switches for configuration.
With your modem, you can add "AT" commands to the software's "modem
initialization string" to configure the modem. Each AT command will "set" 
one "switch". Consult your software manual or your dealer for instructions 
on how to enter such commands.

The chart below shows how AT commands duplicate the function of the DIP
switches, and show the modem's factory default configuration. If you are
experiencing a problem with your modem, particularly if your software 
requires for the settings of Data Terminal Ready (DTR) and Data Carrier 
Detect (DCD).  If you need to change the settings, refer to the chart below.

Dip Switch   Dip Switch    Functions                  Corresponding AT
Equivalent   Settings                                 Command(* = Default)

    1        UP            Modem Follows DTR            AT&D2
             DOWN          Modem Ignores DTR            AT&D0    *
    2        UP            Verbal Result Codes          ATV1     *
             DOWN          Numeric Result Codes         ATV0
    3        UP            Result Codes Disabled        ATQ1
             DOWN          Result Codes Enabled         ATQ0     *
    4        UP            In Local Command State,      ATE1     *
                           Echo Characters
             DOWN          In Local Command State,      ATE0
                           Do Not Echo Characters
    5        UP            Auto-answer On               ATS0=1
             DOWN          Auto-answer Off              ATS0=0   *
    6        UP            DCD Follows Carrier          AT&C1
             DOWN          Forces DCD Always On         AT&C0    *

Many communications programs for PC-compatible computers require &C1 and &D2
in the initialization string: AT&C1&D2

There are other AT commands that can be added to the initialization string 
as well. For example, to increase or decrease the speaker volume, add L3 or 
L1, respectively, to the end of the string.

If you ever want to switch ALL of the settings back to the factory default
configuration, use the command:  AT&F

The following are the most common causes for error:

1) The most common error is that more than one piece of hardware is assigned
to the same COM port, or the communications software is not configured for 
the same COM port as the modem. This can be corrected by making sure that no 
other board installed in the PC has the same COM port setting as the modem, 
and by checking that you have used the correct settings when configuring 
your software.

Note: If you have an external serial port, it will still create a conflict,
even though you are not using it. This holds true for serial ports on added
cards, peripheral devices, and for built-in serial ports. In general, when
PCs have built-in serial ports, they are assigned to COM1, COM2, or both. If
you don't know what serial ports you have, try configuring your modem for
COM3 or COM4; then be sure to configure your communications software to 
match.

2) If all the characters that you type appear twice on the screen, your
communications software may be set for "half-duplex" when it should be set 
for "full duplex". This can be corrected by using your communications soft-
ware configuration menu to change from half to full duplex.

3) Your software's selection of the number of data bits, the parity, and the
number of stop bits is different from the modem that you're calling. You
should normally use 8 data bits, NO parity, and 1 stop bit (8,NONE,1). The
second most common setting is 7 data bits, EVEN parity, and 1 stop bit
(7,EVEN,1). If you call another modem and connect, but get incomprehensible
characters displayed (even after some normal connection noise), try changing
these settings.

4) You are calling a modem set up for one speed, and you are at a different
speed. Some 2400 bps information services have dedicated lines that can only
communicate at 2400 bps. Therefore, if you call them with a 300 or 1200 bps
modem speed you will not be able to communicate. On the other hand, many
bulletin boards and other services will adjust to the speed of the calling
modem.

5) Your communications software has not been set up properly. Re-check the
Initialization String and Dial String specified in your software manual and
in "Setting Up Your Communications Software". Remember that commands in the
initialization string are sent to the modem each time you start your
software.  Many communications programs for PC-compatible computers require
that &C1 and &D2 appear in the modem initialization string.

6) Your software does not allow you to set up the modem to auto-answer in a
sufficiently flexible way. To enable auto-answer without using your software's
menus, use your program's terminal modem and type ATS0=n (where n= the number
of rings to wait before answering). Turn off auto-answer with ATS0=0.

(css 07/28/93)