On 5 Feb 2010 at 18:41, Tony Duell wrote:
Even so, the knoweldge that TTL inputs float high, and
can more easily
be pulled high than low was very well known at the time. Whoever
designed that chip was not thinkibng aobut how it was going to be used
IMHO. I am not talking aobut somebody finding an application later on
for which the original design wasn't perfect, but actually I can't
think of a single applicaiton where the behaviour of the 8255 is
desireable. I can think of some where it doens't matter, but none
where you'd avtually want a chip that behaves that way.
That being said, apparently few think that it's an issue, as a web
search doesn't turn up much in the way of grumbling. But how many
8255s are installed in an application where mode switching is used?
Darned few, I would guess.
The 8255 was obsolete years ago. It's slow and most of the desired
functionality can be gotten more easily with other means, either with
programmable logic or even SSI.
So we're really beating a dead horse.
--Chuck