There are two different pin out variations for the 'P' cable, as found below [singled and paired cable].
One version uses single-ended interfaces [signal and ground] and one version uses differential interfaces [true and inverted signals].
Notice that the signal assignments are almost identical between the two pin out tables.
Ground [a return path] is sent instead of a 'true' signal on the single-ended cable.
The generic representation of the 68 pin connector is shown after the pinout table.
The "A" cable is used with SCSI-1, SCSI-2, or SCSI-3 to provide "FAST"
SCSI with an 8 bit [Parallel] data bus. Refer here for the main SCSI Bus page.
With SCSI-2 the "A" may be used
alone or with the "B" cable to provide "WIDE" SCSI allowing a 16 or 32
bit data bus. The pin-out for the 'A' cable is listed on the SCSI Bus 'A' connector page.
The "B" Single-Ended cable pinout is listed on the SCSI Bus 'B' connector page.
On SCSI-3, the "A" cable may
be used for an 8 bit data bus. However the new "P" cable [shown above] is
used to provide a 16 bit data path (wide SCSI). To allow 32 bits of data
the "P" cable is combined with another new cable called "Q" (wide SCSI).
The "Q" cable pin-out is listed on the SCSI Bus 'Q'
Single-Ended connector or SCSI Bus 'Q'
Differential connector page.
Back to the main SCSI Interface Bus page
The SCSI [parallel] bus width is either 8 bits or 16 bits [Wide bus].
Also the bus may be either Single ended or Differential; however the two
are mutually exclusive SCSI is a chained parallel bus, cables start at
the Host and run from device to device in a chain. SCSI may be used for
asynchronous and synchronous transfers; Asynchronous transfers using
Start and Stop bits and synchronous transfers using system timing
(Hand-Shaking). The data bus also carries one parity bit.
Editor note: The SCSI interface is obsolete, which some might now call the parallel SCSI interface.
The SCSI interface using the 'P' cable, and in fact any cable, is obsolete.
It doesn't matter if the interface is signal-ended or differential, the entire parallel SCSI interface standard is obsolete.
Navigation > Engineering Home > Interface Buses > Cable Buses > SCSI Bus > SCSI 'P' Cable.
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