Specifications
3.5.2
Using
a
Serial
Printer
Serial printers can be connected to the board's PC compatible serial port
as
well.
You can instruct DOS to print to the appropriate serial port
(COMl
or COM2) instead of to
the
Parallel Printer port
(LPTl
or
LPT2) with the DOS
MODE
utility.
For
example, the
following command makes the
COMl
serial device become the system's default printer de-
vice:
A>MODE
LPTl
=
COMl
<Enter>
Now
you can print to the serial printer
as
though it
is
connected to the system's parallel print-
er port.
You can return the printer device to the
Parallel Printer port with the following command:
A>
MODE
LPTl
< Enter >
If
desired, MODE commands can be included in your system's AUTOEXEC.BAT startup me
to assign the printer function to a serial port. Also, additional
MODE
commands can be used
in
other
batch
files to dynamically reassign the DOS printer device function as often as re-
quired during system operation.
Printer
Cabling
and
Setup
The printer must be set for a suitable baud rate, and appropriate data and handshake signals
must be connected between the computer's and the
Printer's serial connectors.
In
particular,
be sure to connect the serial port's "Ready to Receive Data" handshake output signal to the
serial port's Clear to Send
(crS)
input handshake input signal. In addition, the board's Data
Set Ready
(DSR)
input handshake signal
must
be true, for the ROM-BIOS to send output
data, so connect that signal to
an
appropriate handshake output signal from the printer,
or
loop it to the board's DTR output signal.
3.5.3
Using
a
Serial
Modem
Most
PC
communications programs control the serial port hardware directly, rather than
using
DOS or ROM-BIOS functions. When configured
as
described in Chapter
2.
the board's
PC compatible serial port
is
fully compatible with those of standard AT's and
pes,
so all such
software should work properly.
When connecting a serial modem, be sure to connect appropriate input and output handshake
signals, depending
on
what
is
required by the communications software you use. Most
communications programs take care of initializing the serial port baud rate and data
charac-
teristics;
if
not, be sure to use the DOS MODE command to initialize the port.
A number of powerful communications programs are available which can
be used to control
communications applications via a modem. Several of these programs offer powerful "script"
languages which allow you to generate complex automatically functioning applications with
very little programming effort. Examples are:
PCTALK, PROCOMM, XTALK, and
MIRROR.