Specifications
Handshake
Signals
In
addition
to
data
input
and
output,
the
V40 Serial
Port's
RS232C interface includes
one
active handshake
signal
in
each direction
and
one always-true output signal. These
are
typi-
cally utilized as Request
to
Send (RTS) and Clear
to
Send (CTS) signals,
but
can
be
used in
any desired manner.
The
always-true output signal can
be
used by peripherals that require a
Data
Terminal Ready
(DTR)
or
similar static signal.
The
input handshake signal is part
of
the same
I/O
input port that contains the board's SCSI
ID
and
Ooppy configuration bits.
It
appears
as
the
most significant
bit
(bit
7)
of
the
8-bit
read-only
port
at
I/O
address 338h.
The active output handshake signal can
be
driven by one
of
two sources, determined by the
setting
of
a jumper.
One
source is the V40's internal serial controller handshake output sig-
nal, which
appears
on
pin
36
of
the
V40. As
programmed
by
the
ROM-BIOS,
this signal
becomes
true
whenever
the
V40 serial input function is enabled
and
the
input
buffer
is
not
full.
The
other
source for
the
output
handshake signal is
the
printer
port's
-INIT
signal.
If
the
-INIT option is used, it must
be
controlled directly by software
in
a manner appropriate
to
the
application.
Use
of
the -INIT signal for output handshake precludes its normal printer
port
function.
4.6.2
Parallel
Printer
Port
The board's parallel printer port is a Centronics compatible parallel port,
and
is identical in
function
and
interface with that found in a standard PC.
It
has
a data transfer rate
of
up to
approximately 1000 bytes
per
second. Output data and
all
interface control signals are
TIL
compatIble. Note that this
port
does not support data input.
The
logic for
the
parallel
printer
port
is contained within
the
board's
two
ASIC
devices.
IRQ7,the
printer
interrupt,
is
generated
by
ASIC2.
As
in
the
PC, a choice
of
two
I/O
ad-
dresses (278h
and
3BCh) is provided, programmed
by
a jumper option.
If the printer port is not used
in
an
application requiring interrupts from the port,
IRQ7
can
be
disabled
by
a
jumper
option
(W
46), allowing its use
by
external devices
on
the
PC
bus.
The
ROM-BIOS
and
DOS
do not require
the
printer port interrupts,
but
some application
and
utility programs do.
4.6.3
Keyboard
Interface
ASIC2 provides
the
logic for a serial interface compatible with
the
standard
PC
keyboard.
The
keyboard is generally connected
by
means
of
a five-wire cable consisting
of
+ 5 volts,
ground, reset,
and
two bidirectional signal lines, one for
data
and
one for clock.
A keyboard
need
not
be
connected to this port for the system
to
operate.
The
ROM-BIOS
power
on
self test does not halt
if
a keyboard is not found.
4-11