RALPH@UHHEPG.BITNET (11/13/88)
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
wilker@batcomputer.tn.cornell.edu (Clarence W. Wilkerson Jr.) (11/14/88)
For using the z80 SIO, there are several variants , but
the zerox 820 source code should provide a guid. Variants
include the port addresses, whether the two port addresses
are interleaved or not, and how the data rate is set ( this
is external to the z80sio.
For the scsi question, there are lots of scsi controller
boards going on the surplus market for under $100, see
Computer Surplus Store ads in BYTE or Computer Shopper.
Surplus 10 megs drives are about $100. The port to talk
to the SCSI drive is basically a bidirectional parallel
port with several status lines. It is balanced by a
resistor network to about 3 volts.
The pc board approach is used by some tandy coco suppliers,
and I know of at least one such arrangement for Heath Zenith
H89's. The address lines for memory don't have to be selected,
you can just address it via ports, but of course you have
to write the software. The SASI or SCSI software is probably
more generic.dbraun@cadavr.intel.com (Doug Braun ~) (11/16/88)
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 / decwrl \ | hplabs | -| oliveb |- !intelca!mipos3!cadev4!dbraun | amd | \ qantel /
mlinar@caesar.usc.edu (Mitch Mlinar) (11/19/88)
In article <8811140554.AA25836@ucbvax.Berkeley.EDU> RALPH@UHHEPG.BITNET writes: > >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: There are two systems on the market for adding hard drives to a Z80. One is by Ampro which implements SCSI for $180 including software, requiring any SCSI card at the other end. The other is by Emerald Microware which does SASI for $50 including s/w, requiring a Western Digital card at the other end. I have one of the Ampro and three of the Emerald as well as a home-brew SCSI. All work fine. -Mitch
mlinar@caesar.usc.edu (Mitch Mlinar) (11/19/88)
In article <3193@mipos3.intel.com> dbraun@cadavr.UUCP (Doug Braun ~) writes: > >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. > I did the same thing using my Xerox 820-II parallel port to talk to a SCSI board (Shugart SA1610). This one did not require any chips, just cabling. Unfortunately, the cabling is point-to-point to transform Xerox parallel ports into SCSI; also, you can only operate one SCSI card. However, that is enough to run two hard drives. It was a bear to get the timing right. The -I was too slow for writing, but fine for reading which screwed me up for awhile. I also tried an Omti card with the same results. -II, or -I with speedup, is fast enough to keep up on these two cards at least. -Mitch