Abstract: Frequency measure is very important in the design of automatic synchronism equipment.The reason lies in the fact that it exerts a direct influence on the acccuracy of the voltage difference ,phase difference and the quality of cutting-in operations.Taking the ATMEGA128 single-chip processor for example,accroding to author’s experience,two methods of measure are proposed in this article,which would be significant for engineering applications.

Key words: input capture, overflow, interrupt