[Coco] Re: PIA keyboard input?

[Torsten Dittel]

One thing I remember far far away and very darkly about this stuff:

You have to be shure, that the PIA port you're POKEing to is in output
mode, the one you're PEEKing is in input mode (you can set this with
other PIA registers).

Another thing I remember (but this could be a rumour or I just had a bad
dream as a child):

Of course you could this "vice versa": POKEing the rows and PEEKing the
columns. Some games did it that way, and sometimes failed: On early
CoCo-Boards (maybe using the 6820 instead of th 6821?), you could damage
one of the PIA outputs by setting both PIAs to output, setting one as
LOW and the other as HIGH and pressing a key. The damaged port was only
working as an input after that. You didn't notice that from BASIC
(because it always checks keys the way you described it), but those
games doing it the other way failed. Later versions hadn't this
problems, the ports were protected (maybe a feature of the 6821?)
against this "short circuit".

Hmm... thinking about it I guess you could destroy any of that ports
that way, depending where you set the LOW and HIGH states... maybe
nothing more than a nightmare... Hardware gurus out there?

Regards,
Torsten