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Re: Z80 type differences?

Michael Black wrote:

"Tristan Mumford" (nintendologist@nospam.gmail.nospam.com) writes:


G'day.

I have a question that I haven't been able to answer easily. The question
is based on a problem I have.

My poor Apple//e Platimum's Z80 card is dead. Trying to use it locks it
instantly. This is due to a smeared cap that shorted a couple of lines. I
replaced the offending capacitor. There was no damage to the apple.

However the card is still dead. Thankfully it's the standard Z80 Soft
card. And everything is standard and socketed.
First step I'm going to replace all the glue logic chips. If that doesn't
do it there's the Z80B.
It's the only Z80B I have. I have a stack of Z80A MPUs. And there are
Z80-CTC MPUs on eBay. What's the difference and which can be used with the
least modification, if at all?



The "A" and the "B" should denote the speed the CPU can run at.  That was
the case with other 8bit CPUs, and I'm pretty certain that applies to
the Z80.  The reference I have handy came out too early to list such
details, though.

My guess would be the "B" can run faster than the "A", but that might
not be relevant in the Z80 card where the maximum may not be hit.


Not true.  As Knut points out, the B version is a 6MHz part,
and has shorter setup and hold times.  It is these times that
are critical for reliable operation.

There were a few different "Softcards", and the original one
used a clever syncopated clock scheme that worked with the
][ and ][+, but was marginal for the slightly altered bus timing
on the //e.

The //e versions of the Softcard use faster parts to deal with
the marginal timing (just as the //e uses a 2MHz 65(C)02 to deal
with the shorter setup and hold times, even though it still runs
at 1MHz.).

-michael

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