Specifications
In
addition,
the
<
PrtSc
> ("Print Screen") key will
print
the
contents
of
the
video
screen
to
the
LPTl
device. Also, the "Printer Echo" function can
be
used
to
cause all characters written
to
the
console
to
also
be
written to the
LPTl
device.
The
Printer
Echo
function is enabled
with
<Ctrl-P>.
Printer Echo remains enabled until another
<Ctrl-P>
is entered.
3.5
USING
THE
PC
COMPATIBLE
SERIAL
PORT
This section discusses several uses
of
the
board's
PC
compatible
serial
port,
and
provides
some examples
of
typical installations.
Use
of
the
board's
non-standard
V40 serial
port
is
discussed
in
Section
3.6.
3.5.1 Serial Port Initialization
In
general,
before
the
board's
PC
compatible serial
port
can
be
used, it
must
be
properly
configured and initialized. This is sometimes done directly
by
the application program which
will access
the
port's
hardware,
but
is usually
done
as
part
of
the
system configuration
and
boot process.
The
PC
compatible serial port must
be
jumper configured as either the primary
or
secondary
device, as described
in
Chapter
2.
Note
The "COMn"
(n=I,2)
designation is a logical value,
not
a
physical
value.
During
the
system
boot
sequence,
the
ROM-BIOS scans both sets
of
serial
port
addresses,
and
installs the first serial
port
it
locates
as
the
COMI
device,
and
the
second,
if
found,
as
COM2.
Therefore,
if
you
configure
the
board's PC serial
posrt
as
a secondary
port,
it
will
be
installed
as
"COMl",
not
·COM2"!
There
must
be
a
COMI
(primary
serial
port)
device elsewhere
in
the
system
for
an
onboard
secondary
serial
port
to
be
ac-
cessed
as
COM2.
Prior
to
operation, the port's
baud
rate and
data
characteristics must
be
initialized to match
the requirements
of
the external devices that will
be
connected.
One
way to set (and alter)
the
PC
compatible
serial
port's
baud
rate
and
data
characteristics is
by
means
of
the
DOS
MODE
command.
Here
is how you might use the
MODE
command to initialize the primary
port
(COMl)
port to 9600 baud, no parity, 8
data
bits, and 1 stop bit:
MODE
COMl:9600,n,8,l
In
many
cases it is
not
necessary
to
use a
mode
command,
because
the
software which will
operate the serial port
will initialize the port when it loads.
3-5