PORTB + PORTC Interrupt-On-Change

[Amoque]

Yes, quite the "sticky wicket". As I see it, your device must be prepared to capture 9 errors simultaneously- and constantly.

I was mistaken in my first assumptions by imagining something like a frame rate where you would have some measure of time between [machine] cycles to do something. I refer to 3/ above - since there is no measure of time allowed to record the event and no lower limit for the event timing (which, in itself provides some opportunity)... it seems impossible to me. The only hope I see is in "If a subsequent fault condition occur on line 1 whilst the initial line 1 fault is being recorded, and some of these slip through, then that is acceptable - not ideal but acceptable."

The closest "solution" I imagine is 9 processors on a common clock, each recording the status of its input on each tick. This will only work to the limits of the clock speed, but it is a start... Or, you might just use a DSO (of the best speed available) as, in the end, this is the function you describe, is it not?

I have had another thought - what of a decade counter on each line? You would not get specific timing, but at regular intervals you could record the number of faults by reading the counter values.