Troubleshooting with a Frequency Counter

It will tell you if a signal is changing, sure. So it's useful for checking the clocks, and I suppose for seeing if data/address lines are changing at all. But it won't tell you if said data/address lines are doing the right thing. OK, you know the bottom 8 address lines are all changing, but you don't know what addresses the processor is actually acessing, for example. My most-often-used test instrument, an HP LogicDart does display the frequency of the input signal, as well as letting me capture it (high/low/undefined states, not a true 'scope type of capture). I've used that facility for checking clock waveforms, and thus finding the open-circuit crystal in my HP9820. But that reading on its own is not enough to go much further. -tony