Z-80 hack

From: Allison J Parent <allisonp_at_world.std.com>
Date: Sat Aug 7 12:58:03 1999

<Since this is something that's only got to work once, I thought I'd put th
<SRAM on a small scrap of perf, along with a PAL to fiddle with the timing.
<The reason for not fiddling with the nWAIT line is that it doesn't time
<right with the instruction fetches, such that the peripherals will see the
<RETI opcode. If this gets too involved, I'll simply have to suffer throug
<doing it from the parallel port on the PC, but I already have some code
<written many years ago (in BASIC) which does the job nicely, and I'll
<probably never use it again.

Seems like the hard way to get there.

<alignment until these repairs are effected. The code was written for an
<S-100 box I used back in the '80's which ran a 12MHz (hand-picked) CPU

Why 12mhz? Reading the bits directly?

<I found that the wait line doesn't work for this sort of thing. It's got t
<do with the way the peripherals work. Switching the clock rate does work,

It's a way to do it. just dont get clock spikes.

<>I hacked one to 8mhz and then put it back, it was never as solid in
<Their RAM timing was stupid.

It was very reasonable as a 4mhz board. Pushing to 8mhz was too much and
also the rest of the signals smeared out. Mine BTW was a AMPROLB with the
SCSI option.

<What's a TCJ?

The Computer Journal. They are too short on cah to publish but they do
offer back issues.

<I never saw much advantage in using Z-80 with mode-2 interrupts anyway. I
<guess it's just a matter of style. I like simple interrupts, and if it get
<too complicated, use another system to handle the I/O that makes it
<complicated. It's much easier to use three computers than to figure out ho
<to use one with three interrupts. I guess I'm lazy . . .

For many things mode 2 is much to much work. For others it's the only way
to fly. Then again so few CPM machines even used interrupts at all (remember
waiting for the disk to stop before typing?).

I modded my AmproLB for minimum power consumption instead by replacing all
I could with CMOS. The board itself is now under 3.5W power consumption
most of it in the SCSI loads and Floppy.

Received on Sat Aug 07 1999 - 12:58:03 BST

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