Small Computer Systems Interface; Scsi Overview - HP 340 Series Service Manual

Small Computer Systems Interface
SCSI Overview
The DIO-I size HP 98658A SCSI Interface Card is available as Option OIl. It's an interface
providing a protocol that is a standard for a bus which enjoys a growing acceptance with all
types of workstations. Its main advantages lie in its accaptance as a standard, speed and low
hardware cost. It is defined by ANSI standard X3T9.2. Only HP 9000 Series 300 HP-UX Rev.
6.0 and later may be used with SCSI.
SCSI circuits are mounted on a DIO-I accessory card and is installed in the optional DIO-I slot.
Interfacing is done with a 0.5 metre, shielded cable. Other devices are connected in daisy-chain
fashion via shielded SCSI cables which are available from HP in various lengths. An SCSI
terminator is required on the SCSI peripheral to allow proper operation. Figure 3-12 shows a
typical system using the SCSI bus.
SPU
DISC DISC
- terminator
Figure 3-12. A Typical SCSI System
SCSI communicates with peripheral devices across the bus by means of a set of protocols
called HP Common, which is Hewlett-Packard's version of the Comlnon Command Set. These
protocols are implemented in HP-UX revision 6.0 and all later revisions.
The use of disconnect/reselect by the peripherals is strongly encouraged for conventional hard
disks. It is required in the case of lower performance peripherals, for reasons of efficient bus
utilization.
Feature Set
Major features of the HP 98658A SCSI Interface Card are:
• Data transfer rates of up to 1.5 times that of high-speed HP-IB.
• Industry standard hardware and software.
• Access to broad range of peripheral features not offered by HP.
• Many compatible product offerings planned by HP.
• Configuration switches set select code, interrupt level and parity.
62 Functional Description