6502 + ARM micro controller = I don't understand clock cycle

[BigDumbDinosaur]

AdaL wrote:

I concluded the 6502 must have been damaged during soldering...

As Garth said, it's highly unlikely. Consider that reflow ovens reach 450 degrees F and parts are not damaged in that heat. You'd have to lean on the soldering iron for quite a while to get the die that hot.

[rwiker]

AdaL wrote:

Strangely enough, I have seen this weird sequence of reads to $FFFE-FFFF, with some $0000 and $017F randomly appearing, on my very first attempt at moving a breadboard design to perfboard. After days of messing with it and not getting it to properly reset, I concluded the 6502 must have been damaged during soldering, pulled it from the board, put it back into a test rig -- only to see it reset perfectly. I think it may come from an electrical problem, maybe a short somewhere (though I measured no spurious continuity between pins), a brownout from the power supply or a signal path so bad that it distorted the clock beyond any recognition. I don't have an oscilloscope to check anyway.

The CPU was a modern WDC 65c02 from Mouser. Unfortunately I still have no idea what this problem came from. But hey, that's two of us, which makes it a known and documented failure mode, right?

FFFE/FFFF is the IRQ/BRK vector. Maybe you have a floating IRQ pin, or maybe (for whatever reason) most of your reads return $00 (BRK)?

[BigEd]

AdaL wrote:

Strangely enough, I have seen this weird sequence of reads to $FFFE-FFFF, with some $0000 and $017F randomly appearing, on my very first attempt at moving a breadboard design to perfboard.

Welcome, AdaL! It would probably be best for you to start a new thread, especially if you're not building a system with a microcontroller in charge.