In his autobiography, Steve Wozniak recounts his difficulty getting interrupts working on the 6502 microprocessor:
The next step was to debug the 256-byte monitor program on the PROMs. I spent a couple of hours trying to get the interrupt version of it working, but I kept failing. I couldn’t write a new program into the PROMs. To do that, I’d have to go to that other building again, just to burn the program into the chip. I studied the chip’s data sheets to see what I did wrong, but to this day I never found it. As any engineer out there reading this knows, interrupts are like that. They’re great when they work, but hard to get to work.
Finally I gave up and just popped in the other two PROMs, the ones with the “polling” version of the monitor program. I typed a few keys on the keyboard and I was shocked! The letters were displayed on the screen!
Can anyone shed some light on the root cause of the problem? Were the 6502's data sheets wrong?
 Wozniak, Steve. iWoz. W. W. Norton, 2006.