[Coco] PIAs destroyable by software on early CoCo models?

[Roger Taylor]

A general rule has always been that you can't harm any hardware using software.

I wrote a telephone pulse dialer for the CoCo once using the motor on/off 
mechanism, and started playing around with how fast I could get the motor 
relay to switch on and off.  The CoCo 2's and above make a click, while the 
early CoCo 1's were silent.  You can definately hear a CoCo 2 or 3 when you 
switch the relay on and off real fast.  Anyway... this never caused the 
relay to stop working, no matter how I blasted it.  Why in the world was I 
doing this?  I have no idea.  Some projects get out of hand.






At 08:26 AM 12/8/2003 +0100, you wrote:
>Since I didn't get any comments to this one but I'm still curious about
>that, I repost:
>
>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
>
>
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{Roger Taylor}