Vax 613 0S Instruction Manual download pdf (Page 162)

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 Instruction Manual Page 162