NOPs for faultfinding

It’s a reality that a newly built microprocessor board does not work spot-on, or a board gives up the ghost after many years of service. This usually marks the start of a cumbersome search for bad solder joints, broken or short-circuited PCB tracks, defective components or problems with failing software. Such faultfinding jobs can turn out to be very time consuming, particularly if the microcontroller has internal program memory and no external address- or data bus. Considerable extra ‘fun’ is thrown if the operation of the software is not known! Here’s a software solution.