uProcessor fault finder

~Y3 }Processor fault finder When fault finding in a micro- processor system it is not always possible to work in single-step mode, as the processor would then have to stop completely. Not all processors have a wait-input; the Z80 (which is the system we used to evaluate this circuit) has such an input, but with this we get the problem that the refresh of any dynamic RAMs used is lost if the processor is stopped. With the fault finder described here, and the "μProcessor aid" published elsewhere in this issue, both addresses and data can be looked at without the processor having to be stopped for any length of time. Operation is as follows. After the circuit sends a short reset pulse to the processor the program is executed. This RESET pulse is supplied by monostable multivibrator (MMV) IC1a; pulse duration is about 2 μs (the pulse has to be short or the data in the dynamic RAMs might be corrupted). At the same time the second MMV, consisting of IC1 b, is triggered. The duration o...