Scsi Interface; Scsi Bus; Scsi Cable - NEC POWERMATE PROFESSIONAL 9000 Service Manual

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RAIDport connector interface
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Two Wide 68-pin connectors
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One Narrow 50-pin connector
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Subsystem Vendor and Device ID support
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Spin down of SCSI drive
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SCAM (SCSI Configured Automatically) Level 2.

SCSI Interface

The AIC 7895CP also offers active negation outputs and a disk activity output signal.
Active negation outputs reduce the chance of data errors by actively driving both polarities
of the SCSI bus, avoiding indeterminate voltage levels. The SCSI output drivers can
directly drive a 48 mA single-ended SCSI bus with no additional drivers. Synchronous SCSI
can handle up to 15 REQ control signals simultaneously.

SCSI Bus

Each channel's SCSI data bus is 8- or 16-bits wide with odd ECC generated per byte. SCSI
control signals are the same for either bus width. The system board has three onboard SCSI
connectors. Channel A has a high-density, 68-pin Wide connector, and channel B has a
high-density, 68-pin Wide connector as well as a 50-pin Narrow connector. On a 16-bit
wide SCSI bus, the AIC-7895CP assigns the highest arbitration priority to the low byte of
the 16-bit word. This way, 16-bit targets can be mixed with 8-bit targets if the 8-bit devices
are placed on the low data byte. During chip power-down, all inputs are disabled to reduce
power consumption.

SCSI Cable

In systems with a SCSI hard disk drive, a four-connector SCSI cable is routed (in a daisy
chain fashion) from the last internal SCSI device to each subsequent internal device,
including the onboard host controller. The cable can then continue to an optional terminator
card installed in an unused I/O slot on the chassis. From the terminator card, an optional
external SCSI cable can be used to connect external SCSI devices.
Up to three internal SCSI devices can be added to the cable.
For proper operation of ultra/wide SCSI devices, the overall length of the SCSI cable from
the last internal device to the last external device should not exceed 3 meters with four Ultra
Wide SCSI peripherals and 1.5 meters with eight peripherals per channel (within constraints
defined by the ANSI SCSI-3 Specification).
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