That darn Intel jingle...

[Tony Duell]

> 
> On 11/4/2005 at 1:36 AM ard at p850ug1.demon.co.uk wrote:
> 
> >Oh come on. It's broken. Fundamentally.
> >
> >For one thing you can't arbitratily set the direction of individual port 
> >lines (virtually all other parallel chips let you do that). And that 
> >write-to-mode-register-clears-outputs is ridiculous.
> 
> I'll concur with the mode-register write operation as being silly, but
> apparently it doesn't get in the way for too many people.  And setting the

I have long since realised that the worse a chip is, the more liklely it 
is to become popular :-). Same applies to most other things, actually. 

> direction of I/O pins in groups of 8 or 4 is apparently not a stopper for
> most people.    24 bits of mode 0 I/O is pretty cool, no?

Personally, I'd rather have the 20 I/O lines you get from a 6522....

> 
> Consider what the alternatives were back in--what was it--1974? (anyone
> have an exact date?).  You needed parallel I/O, you used an 8212.  The 8255
> was a pretty substantial step forward.   It's pretty amazing that it's
> still around more than 30 years later.

My experience is that if you have an application where there's a fixed 
direction (and no need for the handshake modes of the 8255), it's simpler 
to use the '574 for output and '541 for input. If you want a versatile 
solution, you might as well use one of the better I/O chips. The 8255 is 
somewhat 'in the middle' -- more complex than it needs be for simple 
applications, but not complicated enough for some of the more difficult ones.

> I've seen 8255's hooked to 6800's.  Also trivial to interface there, as
> well as Z-80 and a host of other CPUs.

In a moment of maddness I once linked an 8255 (hey, it was in the 
junkbox...) to the 6809 bus of a CoCo. I got so upset by the misfeatures 
of that chip I went and got a 6522 (which is, of course, trivial to link 
to the 6809)

-tony