Path: utzoo!attcan!uunet!husc6!mailrus!ames!pasteur!ucbvax!UHHEPG.BITNET!RALPH
From: RALPH@UHHEPG.BITNET
Newsgroups: comp.os.cpm
Subject: MEX Overlays and SCSI Implementations
Message-ID: <8811140554.AA25836@ucbvax.Berkeley.EDU>
Date: 13 Nov 88 03:25:00 GMT
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Date: 12-NOV-1988 18:52:57.75
From: Ralph Becker-Szendy RALPH AT UHHEPG
To:   B_INFOCPM
Subj: MEX Overlays and SCSI Implementations
Two questions:

I jost got MEX onto my machine (which is barely compatible to itself, and not
compatible to anything else under the sun). I understand from the MEX
documentation that one needs two overlays: one for the computer-hardware (which
essentially implements the IO), and one for the modem (which implements
commands for dialing, disconnecting and such). I already got the modem-overlays
for Hayes-compatible modems (called SM13 through SM16), so this part is taken
care of. But now I need the "hardware-overlay", and if possible I don't want to
write one myself (doesn't seem to be worth the effort). In the case of Kermit
there is a "generic" overlay which does all the IO via the BIOS entry points
for PUNcher/ReaDeR. Is there a MEX overlay which does exactly that, and could
therefore run on any cp/m hardware with an IOByte and full PUN/RDR support
(like mine)? Such an overlay (although not extremely efficient) would save me a
lot of time. And if there is no "generic" overlay, is there one which just uses
a Z80 SIO (so I only have to patch the SIOs port adress into the overlay? And
if both of these simple solutions don't exist, which  overlay (out of the ones
available via SIMTEL20) should I use as a template write my own (very simple)
overlay?

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