Quote:
Originally Posted by ScottishColin
Two screenshots attached.
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If I'm reading it right, that pin is going cleanly low five times in a row for about 125µs (?) each, about every 17ms; which is exactly what I would expect to see from the sequence 0000-0001-0010-0011-0100-0101-0110-0111-1000-1001 being written to pins 12-15 of UC9.
I'd expect pin 14 to stay low most of the time and periodically make two high-going pulses of 250µs (or at any rate twice whatever the original duration was, if I misread it); pin 13 to stay low most of the time with high-going pulses of 500µs; and pin 12 to stay high most of the time with periodic low-going pulses of 1ms. If you keep pin 15 connected at the same time as the other pin under test, it should be possible to see the relationship between the bits.
This suggests UC9 is getting the right inputs, which is a relief as it means UC7 is probably good. Probing the outputs of UC9 would need resistors adding as discussed above, but I'd happily condemn it on the evidence above alone. Still, if you are feeling sufficiently curious (or masochistic
), each of pins 1-11 (except 8) should show a single low-going pulse of 125µs every 17ms, lined up under one of the ten steps of the pin 15 sequence, if UC9 were good.