Weekend finds - uVAX II w/ SCSI!

From: Eric Smith <eric_at_brouhaha.com>
Date: Sun Dec 12 13:41:53 1999

Chuck McManis <cmcmanis_at_mcmanis.com> wrote:
> 2) It has an NCR53C90 SCSI interface, and 18 nat'l semi 75176BN chips
> wired up to the 50 pin connector. (I'm hoping these are differential
> drivers for FAST SCSI II drives)

There's good news and bad news. The good news is that yes, those definitely
are differential transceivers.

The bad news is that FAST SCSI 2 is *NOT* differential. It's single
ended. 99.9% of the drives you're likely to encounter are single-ended.
Differential and single-ended will not mix [1].

It sounds like this controller will ONLY work with differential drives,
unless they provided some sort of jumper arrangement to bypass the
differential transceivers.

There exist single-ended to differential converters, but they're very

Good luck!

[1] The new-fangled "Low Voltage Differential" (LVD) is different than the
traditional SCSI differential. They cleverly designed most (all?) LVD
drives so that they will work on either LVD or single-ended busses. But
LVD drives will NOT operate on traditional differential SCSI.
Received on Sun Dec 12 1999 - 13:41:53 GMT

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