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Determining SCSI Oscillator Frequency

The TURBOchannel Dual SCSI ASIC (TCDS) has four general purpose input

(GPI) bits, which are readable in its CIR register bits <7:4>. GPI bit <2>

(readable in CIR<6> has been reserved to report the SCSI chip oscillator

frequency. A value of 1 indicates that the oscillator is 25 MHz as in the 300

/400/500 models. When this bit is 0 (for the 600/700/800/900 models), there is a

40 MHz oscillator on the SCSI controller chip capable of Fast SCSI data transfers

if so enabled through the console.

This GPI bit allows a common SCSI driver to run on all 300/400/500/600/700

/800/900 models. CIR<6> will be 0 only on those systems capable of Fast SCSI

transfer rates, with a 40 MHz oscillator.

9.6.3 NCR 53C94 Conﬁguration and Programming (300/400/500 Models)

The 53C94 requires reconﬁguration after a hardware reset for TURBOchannel or

a software reset for the 53C94. The 53C94 has three conﬁguration registers (see

Section 8.3) that must be conﬁgured:

07 000000 0707

MR−0104−93RAGS

00010BID 00001PAR XXXXXB00

Config 1 Config 2 Config 3

Field Value Description

BID 110 Host bus ID

PAR 111 Parity checking conﬁgurations

B 1 Save residual byte

X Reserved

Save Residual Byte Bit

If this bit (see Section 8.2.6) is clear (0), the last byte sent with an odd

transfer count is transfered with a meaningless byte. However, both bytes

are considered data and the meaningless byte may be included in a DMA

transaction to memory. Set the Save Residual Byte bit to prevent this

inclusion.

9.6.4 53CF94-2 Conﬁguration and Programming (600/700/800/900 Models)

The 600/700/800/900 models use a 40 MHz SCSI oscillator and a new backwards

compatible SCSI chip (NCR 53CF94-2) to replace the 53C94 used on the 300/400

/500 models. On the 600/700/800/900 models, the TCDS’s CIR_GPI<2> general

purpose input bit reads as 0 to indicate a 40 MHz oscillator (reads as a 1 for the

300/400/500 models which use a 25 MHz oscillator). The 600/700/800/900 models

also have active terminators (which are transparent to software).

9–16 I/O Programming

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Vax 613 0S Bedienerhandbuch Seite 162