[sebhc] busses and roms

Lee Hart leeahart at earthlink.net
Mon Jun 7 16:15:16 CDT 2004

Steven Parker wrote:
>> are the busses in the H-8 and H-89 at all compatible?

No, they are quite different. The H8 has a true buss, with 50 pins and
all the signals needed for power, memory and I/O.

The H89 has two different buses; one for memory and one for I/O. Each
has 35 pins. This isn't enough to have *all* the signals needed; it
doesn't have all the address lines in the memory buss, or all the pins
for the I/O addresses in the I/O buss.

> Could a card be designed to work for both?

No; but the H89 buses are a subset of the H8 bus. It should be possible
to build an adapter card that allows H89 cards to plug into an H8.

> I know that each had its own version of the H-17 controller, yet
> they share the 444-19 ROM. Aside from the difference in form factor,
> how different are they?

Software-wise, the H89 is an H8 without the front panel. The memory map
and I/O maps are basically the same. It was easy to make software that
ran on both without changes.

> We don't yet have rom images in the archives, but we do have
> listings for MTR-89 and MTR-90.

I have over a dozen H89 ROM images in .hex format. I'd be happy to
provide them. Most of them have no copyright notices either on the part
itself, nor in the code, so I don't see a problem making them available
"Never doubt that the work of a small group of thoughtful, committed
citizens can change the world. Indeed, it's the only thing that ever
has!" -- Margaret Mead
Lee A. Hart  814 8th Ave N  Sartell MN 56377  leeahart_at_earthlink.net

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