Weekend finds - uVAX II w/ SCSI!

From: Jim Strickland <jim_at_calico.litterbox.com>
Date: Sun Dec 12 16:39:04 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
Also, for the difinitive answer on whether your drives are differential or not,
I'd suggest going to www.seagate.com and looking them up. And re: disk drive
depot, their parent corporation does business on the web as www.corpsys.com.

Jim Strickland
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Received on Sun Dec 12 1999 - 16:39:04 GMT

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