Specifications
The board's SCSI interface, and the Ampro SCSIIBIOS within the board's ROM-BIOS are
discussed
in greater detail
in
Chapters 4 and 5.
In
addition application note AAN-8804, avail-
able from Ampro, provides details of the SCSIIBIOS functions available
to
programmers.
2.5.3 Simple Bidirectional
If
0
When
the board's SCSI bus is not needed for interfacing to standard SCSI devices, it can
be
used instead as a general purpose digital input/output port. The SCSI bus
then
becomes a
set
of
programmable
I/O
signals, with
TIL
signal levels and
open
collector
output
drivers
capable
of
sinking
48
mAo
In
this
case,
sixteen SCSI bus signals can
be
used;
of
these, nine
are capable
of
bidirectional
use,
and seven are input-only.
The available
SCSI port output signals can
be
"hit-banged" (i.e. software activated)
to
gener-
ate a wide variety
of
signal timings and operations.
For
example. it is even possible to inter-
face with optically isolated
AC
and DC input and output modules, and
to
a number
of
off-the-
shelf
data
acquisition and control interfaces.
Ampro application note
AAN~1
discusses a typical non-SCSI application. Refer also
to
Chapters 4
and
5 for typical system configuration information, and for technical information
about the board's
SCSI bus interface.
2.5.4 SCSI Interface Configuration
Several items associated with the board's SCSI interface should
be
conftgUl'ed according
to
your system needs:
SCSI
Bus
Termination
Three 8-pin 220/330 ohm SIP resistor networks (RP4, RP5, and RP6) provide bus termina-
tion.
The
termination
networks should
be
present
on
two, and only two,
SCSI
bus
devices.
An
improperly
terminated
SCSI
bus
may interfere with
normal
system
operation
due
to
indeterminate signal levels.
Note
Be
sure
that
the SCSI termination networks are oriented
in
their sockets so that
pin
1 of each
SIP
network, general-
ly marked
with a dot, is
at
the top end of the
board
as
shown
in
Figure
2-1.
Internally, pins 2-7
of
the SIP networks have 220 ohm resistors connected
to
+ 5 volts (pin 8),
and 330
ohm
resistors connected to ground (pin 1).
Note that the
SCSI Bus terminatiOn networks consume significant power (.8 watt).
If
power
consumption is critical, consider having the bus termination external
to
the board,
and
exter-
nally powered.
2-23