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 +---------------------------------------------------------+ | The Apple //'s will live forever!! | | Phil Lindberg snail mail: 13845 S.E. 131 ST | | INET: prl3546@tahoma.UUCP Renton, WA 98056 | | UUCP: ..!uw-beaver!ssc-vax!shuksan!tahoma!prl3546 | | Disclaimer: I don't speak for my employer (and I not | | sure they even know I exist....) | +---------------------------------------------------------+