Damn! The thrill of getting something done evaporates when you see that it works most of the time, but there are cases when it doesn't. Tricky glitches screw you up one in 5 times and that's enough to make it look like crap. When it's all digital (or supposed to be) you expect stuff to work 100% of the time. Take this example. My chip takes a pulse to increment the register pointer. We use a board with push-buttons to generate these pulses. To go from state 0 to state 15, you hit the button 15 times. With software, it's trivial to write a function that takes an argument and goes to a specified state in a jiffy. Problem is, there are times it's off by 1 state - it sometimes rolls over into state 16. You get a feel for the mountain of work involved in testing something before you can sell it. Nothing like having many hands here to make work light. Eyeballs too of course - it's the information age.
In this case, it's looking like the assumption of 100% digital is incorrect. One of the states sends a rather noisy signal to one of the pins and that might mess up my setup that has lots of parasitic inductance in the leads - rather than transmission lines to convey the signals cleanly. Probably a signal integrity thing here. Never had to deal with that before.
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