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From: iverson@bang.uucp (Tim Iverson)
Newsgroups: comp.periphs.scsi
Subject: Re: Always IN-2000 SCSI host adapter (the real story)
Keywords: Always SCSI disk drive controller host adapter
Message-ID: <1991Jun23.055000.4790@bang.uucp>
Date: 23 Jun 91 05:50:00 GMT
References: <1991Jun06.204457.28453@xstor.com> <90@talgras.UUCP>
Reply-To: iverson@xstor.com
Distribution: usa
Organization: SH5
Lines: 60

In article <90@talgras.UUCP> david@talgras.UUCP (David Hoopes) writes:
>In article <1991Jun06.204457.28453@xstor.com> iverson@xstor.com writes:
>>The second problem is much greater: the external connector is not an
>>accepted SCSI-1 or SCSI-2 connector.  It is a 25 pin Macintosh connector.
>
>I am sure that someone will correct me if I am wrong, but I think that the
>Macintosh style conector is an accepted SCSI-1 (I don't know about SCSI-2)

All SCSI-1 connectors are 50 pin.  SCSI-2 has 50 and 60 pin, but no 25 pin.

>>This isn't so bad until you realize that the 25 pin SCSI connectors usually
>>used for the PC have term power and ground swapped w.r.t. the Mac cable.

>This I think is wrong.  I have taken the same drive with cable attached
>and moved it from a Mac to my pc.  In fact that I why we choose to use
>that conector on our SCSI host adapter, so that are tape drives could
>be used on both PCs and Macs with the same cable.

That's exactly the problem I was talking about - *most* PC host adapters
that use 25 pin, have term-power swapped w.r.t Mac pin-outs.  Some don't.
That "some" includes Always, and may bite you in a tender spot (i.e. your
wallet, when you short-out something important).

There are two ways it could have worked anyway with PC-style pin-outs: 1.
your PC's host adapter is one of those that uses the Mac pin-outs; or 2. you
got lucky and none of your devices are supplying term-power to the bus -
could be they're set up to use their own internal source.

If you use 25 pin without knowing the pin-outs or knowing exactly how all
your devices are setup w.r.t. term-power, you're relying on luck.  With 50
pin, you're safe - luck is not involved.

On a slightly humorous note - this problem was discovered accidentally a
couple of years ago by one of our brighter software guys.  About 3 weeks
after he was hired he accidentally used a PC cable for a Mac.  Result: one
shorted out Mac motherboard (it has no fuse).  He did this twice before
that little light bulb we all have lit up - maybe the smell of ozone and
burnt plastic helped.  Anyway, we now call this the "Englebert"-effect ...
name changed to protect the innocent (i.e. me - he knows where I live :->).

>Personally I like this conector better then the 50 pin conector.  The
>little clips on the 50 pin conectors have a bad habit of wigeling loose.

Yeah, I agree - the 50 pin is also pretty big, which sometimes makes it hard
to get the card in the slot without squashing the connector clips, but with
50, at least you don't have to test your cable before connecting it to make
sure the pin-outs are right for the card.

>I don't know anything about the Always IN-2000 and I am not defending it.  I
>just question some of your arguments.

That's okay - they were good honest questions.  BTW - yes, I dodged the chip
question on purpose: it seems to have been answered already (and answered
much better than I could have done).

>David Hoopes                              Tallgrass Technologies Inc. 
>uunet!talgras!david                       11100 W 82nd St.          

- Tim Iverson
  iverson@xstor.com -/- uunet!xstor!iverson