Specifications
5.6.2 Simple 8ldirectionaillO
If
you
plan
to
program
the
53CSO
yourself, you will
need
a copy
of
the
NCR
53C80 design
manual mentioned above.
The
53C8O
has 17 bidirectional 110 lines, which
may
be used as
inputs
or
outputs under software
contro~
and also offers the option
of
a variety
of
interrupts
based
on
specific transitions
of
110 signals.
Basically,
the
53C80
has
two operating modes:
Initiator
and
Target
modes.
In
Initiator
mode, several conditions
are
required before
data
output to the 110 bus
can
be
active.
If
the
device is
used
in
the
Target
mode, however,
these
special conditions
are
not
applicable.
Consequently, the 53C80's Target mode results
in
more flexible operation for simple bidirec-
tional
110.
The
53CSO
is placed
in
Target
mode
by
writing 40h
to
the
Mode
Register.
Once
in
Target
mode, all 17 110 signals except
ACK
and
ATN
may
be
used as
both
inputs and outputs.
In
Target mode,
ACK
and
ATN
are inputs only.
The
data
lines (DBO-7,P)
are
outputs when bit
o ("Assert
Data
Bus")
of
the
Initiator Command Register is a 1, and inputs when bit 0
of
that
register is a
O.
It
is also possible to utilize the 53C80's internal interrupt generation logic to perform inter-
rupt-based
I/O
with the device.
One
user has taken advantage
of
this feature to monitor and
store the
data
transmitted
by
a Centronics type printer port
of
a computer, using the SCSI bus
interface as
an
interrupt-driven 8-bit input port.
Three
additional input bits, normally used to indicate SCSI
ID
to the ROM-BIOS,
are
avail-
able for
110 input via the
Jumper
Input
Port
(discussed below).
The
other five
Jumper
Input
Port
bits can
be
used for general purpose inputs,
if
they
are
not used for their normal func-
tions.
The
parallel
printer
port
can
also provide
an
additional
set
of
eight
outputs
and
five
handshake signals,
if
it is not required as a printer interface.
Refer
to
Ampro
application note AAN-8801 for additional information
on
bidirectional 110
use and programming
of
the SCSI hardware.
5.6.3
Jumper
Input
Por1
This port reads eight signals. Seven
of
this port's eight bits reflect the state
of
seven
jumper
pairs
(W23-W29); the
eighth
bit reflects
the
state
of
the
input
handshake
signal
of
the
V 40
Serial
Port's RS232C connector.
The
status
of
the
Jumper
Input Port is sensed
by
reading 110 port 338h.
The
low
order
seven
bits
of
this
port
reflect the jumpering
of
the seven pairs
of
pins at the locations labeled W23-
W29
on
the
board.
The
input
data
for
these
bits will
be
0 (low)
when
the
corresponding
jumper
is
in, and 1 (high) when the
jumper
is
out. Bit 7
is
the RS232C input handshake for
the
V 40 Serial Port.
Table
5-6
shows the functions
of
the bits
of
the
Jumper
Input Port.
If
it
is not needed for its
intended uses
by
the board's ROM-BIOS, the
Jumper
Input
Port
can also
be
used for general
purpose
data
input.
5-8