Path: utzoo!attcan!uunet!cs.utexas.edu!csd4.csd.uwm.edu!bbn!mit-eddie!uw-beaver!ssc-vax!shuksan!tahoma!prl3546
From: prl3546@tahoma.UUCP (Philip R. Lindberg)
Newsgroups: comp.sys.apple
Subject: Re: Homebrew SCSI pitfalls
Message-ID: <550@tahoma.UUCP>
Date: 14 Aug 89 15:43:21 GMT
References: <1431@esunix.UUCP>
Organization: The Boeing Co., BCA FSL, Seattle, WA
Lines: 47

From article <1431@esunix.UUCP>, by jsnow@esunix.UUCP (John Snow):
> Here is a word of warning to those of you building homebrew SCSI drives
> for the Apple II family.  APPLE VIOLATES THE SCSI SPECIFICATIONS for
> terminating the SCSI bus!  The SCSI spec requires that the SCSI bus be
> terminated by 220/330 resistors at BOTH ends of the bus.  The Apple II
> SCSI interface card does NOT terminate the cable.  Apple normally gets
> away with this violation by supplying a very short SCSI cable to connect
> the SCSI interface card to the first disk drive where the SCSI cable IS
> terminated.  This is poor design practice but normally works.
> 
> I purchased a SCSI cable from Tulin along with a Tulin A-hive case and power
> supply.  The SCSI cable Tulin sent me was 6 feet long -- much too long to

This is very interesting.  I have a "homebrew" SCSI drive with a Tulin
A-hive case and a 6 foot SCSI cable (I bought from Tulin with the case).  I
have experienced no problems with my drive.  It has been running for about
2 months now, with power up and down two or three times a week.

> termination was the problem.  I hacked the 6 foot cable down to 18 inches
> and wired on a new connector and what do you know, it works!
> 

Have you considered that maybe you had a bad cable, since when you replaced
it it worked okay?

> What would it have cost Apple to terminate things properly, less than a buck
> to put in the resistor packs and sockets to allow them to be removed if the
> CPU was not at the end of the cable!
> 

This is not to say that you aren't correct on your assumption that Apple
didn't terminate things correctly.  It's just that I have not experienced
any problems with the same original setup.

Phil

> John F. Snow


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|  Phil Lindberg	    snail mail: 13845 S.E. 131 ST |
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