Barry Gershenfeld wrote



>I found that CPU's rarely go bad (unless you force them to).  This is,=20
>maybe
> the third bad Z80 I've run into.
>
> I wanted to mention, that in my experience, with no EPROM installed, the=
=20
> CPU
> reads FF, and if I recall correctly that is an RST 7. More importantly, I
> remember seeing the same "counting behavior" on the address lines as
> everyone else was trying to produce.  You should try this since it's as=20
> easy
> as pulling the EPROM.   Before I realized your chip was socketed I was=20
> going
> to suggest breaking just the chip select pin--it should produce the same
> thing.
>
> My guess about the "counting behavior" was that it continually tries to=20
> push
> to the stack, and the stack pointer is put on the address lines each time
> this happens.
>
> I still have an EPROM burner.  Is this a rare thing yet?
> --=20

I had tried looking around while running with the eprom pulled, but the=20
waveforms weren't as 'clean' as when I fitted the nop adaptor.

I only recently bought an old  Dataman S4 burner off ebay and have used it =
a=20
lot. About a hundred chips so far. Surprisingly useful, though finding=20
blanks of the old chips eg 2716 etc is difficult.

In fact in searching through my Z80 stuff I came across two 2716's in a box=
=20
with an eprom burner I built myself back when I was studying processors 25=
=20
years ago.

The Dataman has been handy to make copies of the eproms fitted to boards=20
that come in, even if it is just a file stored on my pc. It's surprising ho=
w=20
often people send me a board to repair with no eprom  ...   how am I=20
supposed to run it and fix it without one???

Regards,   Roger=20

--=20
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