There is a lot easy way of dealing with this problem if you do some research. A lot has already been done with the 80C51 and frequency counters. Simply find a working model, copy that, learn from it and then change what you want.

Anyway it sure teaches you how this stuff really works when you sit down and do it yourself.

I diasagree, 'Learning' this way has proven very inefficient, all you learn is copying, trying to understand the issues top down, instead of bottom up will not get you to any real understanding.

I recommend the following: "work on the issue, then work some more and when you, yourself have come close THEN, do as Charles suggest.

Of course, if you have no interest, whatsoever, in learning anything just go ahead and copy some stuff from the net. but then, good luck if you find a problem, you will not have even an inkling what to look for.

Erik