HP 340 Series Service Manual page 75

Unsupported SCSI Attributes
Differential Drive. Both single-ended and differential drive are part of the SCSI standard.
However, the Model 340 SPU's SCSI option supports single-ended drive only.
Slow Devices. There is no intention of providing multiple SCSI busses in order to accomodate
peripherals that utilize the bus inefficiently. The word "inefficient" can be quantified by defining
these three classes of peripherals:
Class Description
2 Bursts data in asynchronous or synchronous modes at a minimum of 1.5 megabytes per
second.
Disconnects from bus if needed such that no dead time in excess of 5 milliseconds is created
on the bus.
:Maintains an average data rate in excess of 1 Mbyte per second after data transfer starts.
Does not hold the bus longer than 100 milliseconds in normal operation.
1 Bursts data in asynchronous mode at a minimum rate of 1 Mbyte per second.
Disconnects from bus if needed such that no dead time in excess of 40 milliseconds is created
on the bus .
. Maintains an average data rate in excess of 400 Kbytes per second after data transfer starts.
Does not hold the bus longer than 200 milliseconds during normal operation.
0
Any peripheral not meeting Class 1 specifications.
'Normal operation' is defined as a 16 Kbyte read or write for a random-access mass storage
peripheral. For a physically streaming device, it is operation in streanling mode. For devices
such a printers and optical scanners, it is continuous operation at full mechanical speed for the
device.
Class 2 peripherals are preferred. Class 1 are acceptable, if a significant price advantage exists
for a partjcular device. Class 0 devices are not supported by the SCSI card.
SCSI versus HP-IB
SCSI hardware in combination with HP Common is analogous to HP-IB hardware and CS80.
The SCSI standard provides data transfer rates of up to four times that of HP-IB. Here are
some other differences:
Interfacing to Peripherals. SCSI is limited to eight devices. With the SCSI card implementation,
that means one mainframe and up to seven peripherals. By comparison, HP-IB is limited to 31
devices.
Termination. The SCSI bus must be terminated at both ends. HP-IB does not require
termination.
Chaining. SCSI devices must be connected in daisy-chain fashion. HP-IB devices may be
connected in any configuration, that is, chaining, starring or any combination . .
Specific Connectors. Connection to the SCSI bus is by a 50 pin micro-ribbon cable with shielded
connector. The HP-IB connector is a 24-pin D-style connector configured in two rows of 12 pins.
Functional Description
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