Hello Jan,

Jorge is running into all of the problem getting a 80C51 working as a frequency counter. The limitation of a 12 clock and two clock minimum pulse width limit the upper frequency to 1 megahertz at a clock speed of 24 MHz but those problems are minor when you don't have anything working.

One step at a time. First get something working as a frequency counter. Second problem he most likely will run into is converting the 24 bit binary value into something that can be displayed. It sounds like handling the 16 bit timer counter interrupt was going to bug him a while.

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.

Good luck,

Charles Bannister