Re: Interesting C64/6526 case

On Fri, Oct 26, 2018 at 4:48 PM <silverdr@wfmh.org.pl> wrote:
>
>
> > On 2018-10-26, at 16:33, Francesco Messineo <francesco.messineo@gmail.com> wrote:
> >
> >>> Now to the interesting case. I've got a CIA that passes all the
> >>> diagnostic tests,
> >>
> >> My impression is that in general the tests aren't that throughout and
> >> can miss stuff.
> >
> > This is surely the case. It's a complex task to very well test a
> > Complex Interface Adapter ;)
>
> True. Just here those are simply port bits. I'd need to check if there is a way to test those both directions. Maybe it's tested only one direction. And maybe there is no easy way to test it both directions. But if there is, and it's not tested that way then this is another point to add to my list of things to improve in the test cart's software I use.

if you have a way to at least loopback I/O pins to other I/O pins
(like on the user port with an external adapter for example, or
substituting a loopback connector in place of the keyboard connector)
then you can test the pins on both input and output functions,
however, it would require much more effort to test output current
capability and input logic thresholds, I'm sure you know what I mean.
Looping back I/O pins to other I/O pins on the same device can give
you an idea of what's surely broken and what might be working, but can
not give final results of all possible failure modes.
Frank