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Chapter 3 - Software Configuration
3.4.1 Changing Default Parameters
By default, the modem will answer after the first ring and try to communicate with a modem on the
other end of the line. If you have one telephone line for voice, fax, and modem communications, the
modem may attempt to answer all incoming calls, voice as well as data. To change auto-answer to
default off, open your communications program and type the following string in the terminal window:
AT &F S0=0 &F9 &W0 <CR>
This string selects the factory default parameters, then turns auto-answer off and stores that setting,
along with all other current parameters, in nonvolatile memory. The &F9 command causes the
modem to load the values from nonvolatile memory the next time it receives the &F command. You
will use the same initialization string as before:
AT &F X4 ^M
But now the modem will load the values stored in nonvolatile memory when you turn on the modem
and when you issue the ATZ or AT&F reset commands.
Note: Because it clears the command buffer, you should not use ATZ in an initialization string.
3.4.2 Other Parameters
The default values for the other parameters in modem configuration menus rarely need changing.
They typically include the dialing prefix (ATDT for touch-tone service and ATDP for rotary service),
the dialing suffix (^M), the hang-up string (+++ATH0^M), and response messages (
RING, NO
CARRIER, BUSY,
etc.). Communications software with a host mode might also include an auto-
answer string (AT S0=1^M).
3.5 Configuring Software for Your Computer
You must configure your communications software to match your computer’s configuration. If the
modem is connected to the COM2 serial port, you must tell the software you are using COM2.
Another important parameter is the serial port baud rate. This is the speed at which your modem
communicates with your computer,
not
the speed at which your modem communicates with another
modem. When V.42bis data compression is enabled, you must have a serial port baud rate four
times the transmission speed of the modem to fully optimize compression. So if your UART is fast
enough, you should set the serial port baud rate to a
minimum
of four times the top speed of your
modem.
If you have an 8250 UART, your most reliable serial port speed will be 9600 bps; if you have an
8250A or a 16450 UART, try 19,200 bps; if you have a 16550 UART or equivalent, a serial port
setting of 115,200 bps can be set reliably.
3.5.1 Configuring Software for the Remote System
You must meet the requirements of the remote system for successful communications. Though the
modem can automatically match the speed of the other modem, you must specify parameters such
as type of flow control, break length, number of data bits, number of stop bits, and parity. If you set
these parameters incorrectly with the remote system, gibberish will appear on your screen.