Specifications

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As its name implies, the SCSI/BIOS consists of a set of low level functions which have been
incorporated into the ROM-BIOS to provide a hardware independent interface between system
software and peripheral devices connected to the SCSI bus. The advantage of the Ampro
SCSI/BIOS is that programmers can write software that uses devices connected to the SCSI bus
without having to be concerned with the details of operating the board's SCSI bus interface. Also,
software can be "ported" to the Little Board/286 from other hardware environments much faster due
to the presence of the SCSI/BIOS, and with less difficulty and risk.
The board's SCSI interface, and the Ampro SCSI/BIOS within the board's ROM-BIOS are
discussed in greater detail in Chapters 3 and 4. In addition application note AAN-8804, available
from Ampro, provides details of the SCSI/BIOS functions available to programmers.
2.5.3 Simple Bidirectional I/O
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 TTL signal levels and open collector output drivers capable of
sinking 48 mA. 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 "bit banged" (i.e. software activated) to generate a
wide variety of signal timings and operations. For example, it is even possible to interface 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-8801 discusses a typical non-SCSI application. Refer also to
Chapter 3 for typical system configuration information, and to Chapter 4 for 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 configured according to your
system needs:
SCSI Bus Termination
Three 8-pin 220/330 ohm SIP resistor networks (RP4, RP5, and RP6) provide bus termination.
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, generally
marked with a dot, is at the top end of the board as shown in
Figure 2-1.