Using Atmel ATF22V10CZ PAL in servo amp, as Hall sensor decode for motor commutation. Logic is strictly combinational (no clock used, no feedback from outputs to inputs 'cept through motor, via motion). Used power down version of PAL cause Hall state transitions are slow, by electronic standards, and the power savings were nice, if not absolutely necessary.
Problem I'm seeing is, once in a great while, PAL "forgets" to change output state in response to change in Hall lines. Result not too hard to catch, in post mortem, 'cause motor stalls, then waits patiently at "zero torque" point for hapless engineer to attach scope probe to drive PCB. Result is clear: PAL outputs and inputs don't match source code file. But, if you "nudge" motor to next Hall transistion, resumes normal operation ,and PAL pins show expected logic levels, all six legal Hall states, 'till the next failure event.
Was concerned that the rise times on the Hall signals might be too slow for reliable triggering of "Atmel's patented Input Transition Detection (ITD) circuitry" since the Hall sensors are Open Drain devices. So, decreased pull up resistor from 10K to 1K, reduced capacative bypass from 0.1uF to 0.01uF. No help.
Any idea what the gremlin here might be? Should mention, this symptom shows up in about 20% of drives built to date. Going through the exercise now of peeling off checksum labels and checking date codes, to see if we might have a bad batch of PALs!
W Letendre