Hello Mr. Sunny CHU,

There are two sites which have information about frequency counters using a 8051 type CPU.

The first is located in the code library. (http://www.8052.com/codelib.phtml)

It is entitled "Frequency Counter by Thomas Zepf, A frequency counter, Determines the frequency of the input on a given I/O line."

The second is located at the below site address. It is entitled "Microcontroller makes effective frequency counter"

http://www.e-insite.net/ednmag/in...76&stt=001

Good luck,

Charles Bannister