Scsi Controller; Scsi Bus; Register Access - Performance Computer PT-VME161 User Manual

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Section FUNCTIONAL DESCRIPTION

SCSI Controller

The Emulex FAS126 Fast SCSI Processor Chip is a high performance CMOS device that conforms to
the ANSI standards, X3.131-1986 (SCSI-1) and X3T9.2/86-109 Rev.10c (SCSI-2), for Small Computer
Systems Interface (SCSI). An 8-bit bus provides FAS216 register Access to the 68060. The FAS216's
internal sequencer is capable of performing common SCSI algorithms, or sequences, in response to a
single command, thus reducing the SCSIbus protocol overhead.
The FAS216 uses a register superset of the NCR 53C94 used on the PT-VME131 to provide SCSI-2
functionality. This compatibility offers the user an easy upgrade to SCSI-2 performance.
The FAS216 is permanently strapped in Bus Configuration Mode 2 (dual bus, multiplexed, byte control,
16-bit DMA transfers). Also, because of the hardware implementation, the "Alternate DMA mode"
option in FAS216 Configuration Register 3 must not be enabled.
The FAS216 is driven with a 40 MHz (25 ns.) clock. Various programmable parameters derive their
timing from this clock.

SCSI Bus

The FAS216 incorporates on-chip 48 mA drivers for single-ended (TTL) transmission. It is capable of
operating at a sustained data transfer rate of up to 5 megabytes per second (SCSI-1) and 10 megabytes
per second (SCSI-2) synchronous modes or 7 megabytes per second in asynchronous mode. Parity gener-
ation and checking is optional on all SCSI bus transfers.
The SCSI interface is through the P2 VME connector. Termination is provided by optional plug-in
resistor packs. The resistor packs should be installed if the PT-VME161 is at either end of a SCSI cable.
Conversely, the resistor packs should be removed if the PT-VME161 is installed in the middle of the
SCSI cable.
The local SCSI termination circuit draws its power from the SCSI TERMPWR signal [TPWR]. Jumper
K6 determines whether the PT-VME161 sources SCSI TERMPWR [TPWR] (pins 1-2 shunted) or not
(pins 1-2 open).
A 1 amp fuse (Littelfuse 273-001) protects the SCSI termination power [TPWR] from short circuit condi-
tions.
For more information see " SCSI Termination" on page 17 and " SCSI Considerations" on page 23.

Register Access

The sixteen internal register locations of the FAS216 reside at locations 0A000000h through 0A00000Fh
in the 68060's address space. They are accessed through the 8-bit Buffered Data/Address bus attached to
bits <24:31> of the Microprocessor Data Bus. The PT-VME161 incorporates logic that invokes the
dynamic bus sizing mechanism of the 68060 forcing byte operations on any size reference to the 8-bit
Buffered Data/Address Bus.
54 Extensible Single Board Computer/Controller User's Manual