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Newsgroups: comp.sys.apple2 Path: news.uiowa.edu!chi-news.cic.net!newsfeed.internetmci.com!in2.uu.net!comp.vuw.ac.nz!actrix.gen.nz!dempson From: dempson@atlantis.actrix.gen.nz (David Empson) Subject: Re: RAMfast to SCSI cable Message-ID: <DJCyJ1.MAx@actrix.gen.nz> Sender: news@actrix.gen.nz (News Administrator) Organization: Actrix - Internet Services Date: Sun, 10 Dec 1995 06:40:13 GMT References: <4a44d8$l7p@newsbf02.news.aol.com> <4acd19$l9o@newsbf02.news.aol.com> X-Nntp-Posting-Host: atlantis.actrix.gen.nz Lines: 68 In article <4acd19$l9o@newsbf02.news.aol.com>, RUBYWAND <rubywand@aol.com> wrote: > In article <DJ9rpL.CM0@actrix.gen.nz>, dempson@atlantis.actrix.gen.nz > (David Empson) writes: > > > >If you make any mistakes with a SCSI cable, you are likely to damage > >the SCSI card as well as the drive mechanism (a friend of mine managed > >to blow up a SCSI mechanism by plugging a cable in upside down). > > When the CD-ROM unit arrived w/o a cable, an order was placed right > away ($9.95 + postage). Then, it occurred to me that such a cable might > be pretty simple to make. IF Sequential designed their 25-pin connection > for a convenient ribbon cable match to the 50-pin SCSI plug, then > alternating lines might go to top and bottom SCSI pins starting from one > end of the plug. Definitely not. The RAMFast should use the same pinout as the Mac and Apple's own SCSI cards. The cable pinout is documented in the technical reference manual for the Apple High-Speed SCSI card (and the original one as well). This pinout is not a simple mapping from one end to the other. I repeat that it is NOT easy to make one of these yourself. Apart from any issues of wiring errors, you also need a properly shielded cable to minimise noise being picked up or radiated. You should definitely not use a ribbon cable. Here is the pinout, assuming I haven't made any typos (I can't see any). DB-25 50-pin Function 1 49 -REQ 2 46 -MSG 3 50 -I/O 4 45 -RST 5 44 -ACK 6 43 -BSY 7 16,18,19 Ground lines 8 26 -DB0 9 20,21,22 Ground lines 10 29 -DB3 11 31 -DB5 12 32 -DB6 13 33 -DB7 14 1,2,3 Ground lines 15 48 -C/D 16 4,5,6 Ground lines 17 41 -ATN 18 7,8,9,11 Ground lines 19 47 -SEL 20 34 -DBP 21 27 -DB1 22 28 -DB2 23 30 -DB4 24 23,24,25 Ground lines 25 38 TERMPWR The unlisted pins in the 50-pin connector (10, 12, 13, 14, 15, 17, 35, 36, 37, 39, 40, 42) are ground. Note: the numbers for the 50-pin connector are counted along each row, like a DB-25. They are NOT the wire numbers in a ribbon cable. -- David Empson dempson@actrix.gen.nz Snail mail: P.O. Box 27-103, Wellington, New Zealand