cctech Digest, Vol 78, Issue 3

Tony Duell ard at
Fri Feb 5 12:41:06 CST 2010

> On 4 Feb 2010 at 19:15, Tony Duell wrote:
> > That's the one. A more stupid design decision is hard to imagine!
> Okay, in Intel's defense, are there any earlier peripheral chips for 
> the 8-bit bus  (I don't count the 8212 and the 8205)?

When did the 6820 come out?

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.

> ...and here we are, more than 35 years down the road and you can 
> still buy the things new.  Say what you want about it--it's probably 
> one of the most durable peripheral chips out there.

And I am still wondering why...


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