Weekend finds - uVAX II w/ SCSI!

From: Chuck McManis <cmcmanis_at_mcmanis.com>
Date: Sun Dec 12 16:08:10 1999

At 07:41 PM 12/12/99 +0000, Eric Smith wrote:
>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].

Well, I "liberated" a couple of 2+ GB drives (Seagates) from a Sun 490 disk
tray that suggest they are differential SCSI. I could live with 4GB :-).
Its intereface termination resistors are plug in sips. I wonder if they
used the trick where you replace the four rows of sips with a single DIP
terminator to switch it to an SE bus. TransTech still has a web site but so
far no word from their Support email.

Another interesting bit is that it is a QDT so presumably it is disk and
tape, but I don't think I've ever seen a differential tape drive. Perhaps
they assume the tape drive has the converter on it.

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

To be determined.

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

Actually I recall that Disk Drive Depot sells them fairly cheaply. (less
than $20 as I recall)

--Chuck
Received on Sun Dec 12 1999 - 16:08:10 GMT