Date : Tue, 15 Nov 1988 17:59:06 GMT
From : blake!ogccse!littlei!omepd!mipos3!cadavr!dbraun@beaver.cs.washington.edu (Doug Braun ~)
Subject: MEX Overlays and SCSI Implementations
In article <8811140554.AA25836@ucbvax.Berkeley.EDU> RALPH@UHHEPG.BITNET writes:
>I am comtemplating adding a hard-disk to my system.
>There isn't anything on the market (no surprise in the case of a self-built
>computer with a non-standard bus). I see two good options:
(option a. deleted)
>b. Build my own SCSI controller. As far as I understand SCSI is
>just a glorified parallel port and an interface definition. There are
>(supposedly) dedicated SCSI controller chips. And one could add DMA (with the
>Z80-DMA chip, or with the built-in DMAs in the Z280). Advantage: nice, clean
>design. Can be made to be real fast (DMA). Can implement a real nice driver in
>the BIOS. Can connect more than just disk drives to the SCSI bus (tape drives
>and laser printers come to my mind). Disadvantage: Lots of work. SCSI disk
>drives are more expensive. Again, who has experiences with this? Which
>SCSI controller chips and disk drives are recommended?
I did just this for my one-of-a-kind CPM system, and it has worked out
very well. The SCSI Host Adapter is indeed a glorified parallel port,
and I built one from 6 or so TTL chips. If you used one of those SCSI
controller chips, the design wuld probably be even simpler.
For a controller, there are several places to get SCSI-to-ST506 controller
cards. I have one made by Shugart (before they went away). There
are several others readily available, for about $80 or so. I have
also had a SCSI tape drive hooked up to my system. This was very easy to do.
I also use the same controller (I have two) on a PC with a PC host adapter.
If this approach sounds worthwhile to you (or anyone else), send me mail,
and I will tell you more.
Doug Braun Intel Corp CAD
408 765-4279
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