[sebhc] 444-66

Lee Hart leeahart at earthlink.net
Sun Jun 20 00:35:46 CDT 2004

Peter wrote:
> The trick with speeds over 4MHz was to implement speed switching
> in the OS. When the computer needs to access certain hardware,
> I would have it switch to 2MHz operation till the I/O was completed.
> This was not necessary for a 4MHz mod.

As I recall, at 4 MHz the hard-sector code was the only thing that
required some patches.

On our H-1000, we had the hardware switch to 2 MHz during any I/O cycle
or on accesses to the ROMs or static RAM (i.e. the H17 ROM or "floppy"
RAM). This meant that no software patches at all were needed to run at 4

> Although I have not done it successfully myself, I have had
> reports of some users running at 8MHz. I don't remember any
> more who did this - it was quite a while ago.

Our H-1000 could run its Z80 at 8 MHz, but its hardware was slightly
different than the original H89 CPU board. A few patches were needed in
CP/M and HDOS to run it at 8 MHz, besides the above mentioned trick of
dropping to 2 MHz for I/O and ROMs. But there were quite minor. Heath's
software was remarkably tolerant of CPU speed.

But, I never did try to get the Heath CPU board to work at anything over
4 MHz.

> As for the 444-66 source, I do not have it.

I do, and a PROM programmer that can program them as well. However, the
parts I have are the stock speed.
"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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