Date : Mon, 14 Nov 1988 19:15:39 PST
From : rzh@freedom.llnl.gov (Roger H. Hanscom (415) 423-0441)
Subject: HD and controllers for the Z80
>Two questions:
> (A MEX question)
>Part two is more of a hardware question, and does not REALLY belong on
>INFO-CPM. I'll ask anyhow: 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:
>a. Buy an IBM/PC (8-bit bus, not AT) disk controller, and just adapt the bus
>signals (and connectors, of course) to interface it to the Z80 bus. Obviously
>I'd have to disable the PC BIOS ROM on the controller card, and I'd have to
>find out the low-level commands for the disk controller. Advantage: real
cheap.
>Disadvantage: No DMA; and it's a kludge; and my machine may get AIDS from the
>PC (aargh) hardware. Question: Does anyone have (good or bad) experiences with
>using PC periphereals on a Z80 based system? Which controllers are good to use
>(for example, well enough documented)?
>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?
>Suggestions (and requests for a summary of all answers) to
>Ralph Becker-Szendy RALPH@UHHEPG.PHYS.HAWAII.EDU
>University of Hawaii / High Energy Physics Group RALPH@UHHEPG.BITNET
>Watanabe Hall #203, 2505 Correa Road, Honolulu, HI 96822 (808)948-7391
No help on Part I here, and Part II DOES belong in INFO-CPM! Look in back
issues of MicroCornucopia --- say about March-April or May-June 1987. Dave
Hardy devoted one of his last S-100 columns to plans for a wire-wrapped
HD interface for the S-100 buss. He used a Western Digital generic con-
troller (can't remember the number, but I can get it for you if you want),
and the S-100 part was just a bi-directional parallel port to get data
and commands to and from the WD card. The WD card can handle up to 2
ST-506 drives (you know, "IBM compatible") that are less costly than
SCSI, I think. I was very interested in his design, but the one place
that advertised this generic WD controller wants about $180 for it. That's
way too high when one can buy a PC controller for way less than half that!!
I wrote to him, and asked him about using a PC controller, and hacking it
around to work, but he never responded. The generic WD card is *ONE* way
to go. There is also a HD kit for the Z80 that apparently uses a little
"daughter" board that plugs into the existing Z-80 socket. This comes
with the WD generic controller and "software". Definitely the "easy"
way to go, but not easy on the wallet -- $500 range. I can get you
that address if you're interested. Don't know if it uses DMA. I might
be biased here, but I'd avoid dealing with SCSI if I could. Too costly.
You can pick up an ST-506 drive (10-20M) for relatively little. See if
you can find Dave's article. It'll give you some ideas!!
Roger
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