Re: Strange 8255 behavior

From: Michał Pleban <lists_at_michau.name>
Date: Thu, 14 Jun 2018 14:48:51 +0200
Message-ID: <5B226433.4040602@michau.name>
Francesco Messineo wrote:

> the 1508 has 128 macrocells, the EPM7256E has 256 macrocells.
> An ATF1502 can fit a 24 I/O pins with separate DDR control on each
> pin, it's in the
> examples of wincupl.

That's for sure, but 6526 is much too more than a few I/O chips. You
have two 16-bit counters, interrupt logic, TOD clock, serial port etc.
All this uses macrocells - basically you need to counf one macrocell for
every bit that is being latched in aby way, plus extra macrocells for
some decoding logic etc. I counted all the latches in the 6526 once and
the result was more that 128.

I wasn't aware of the 256-cell CPLD though, I work with the Ateml ones.
That one might be big anough, but can you still purchase it in bigger
quantities? The Atmel chips are still being made, wheread the Altera one
have been discontinued long ago.

Regards,
Michau.
Received on 2018-06-14 15:01:58

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