Learned that one the hard way. I built a 6502 single board computer and tested it out running my customer built monitor. I spent hours verifying the hardware t

Learned that one the hard way. I built a 6502 single board computer and tested it out running my customer built monitor. I spent hours verifying the hardware to isolate a problem where programs would crash and memory would become corrupted. Turns out my monitor was popping garbage into the flags register when it returned control and sometimes setting decimal mode.