DETECTION METHOD FOR ALTERNATING POWER FREQUENCY

摘要

The frequency of AC power is used as external interrupt signal for a microcomputer and is counted by an internal counter to exclude the usage of frequency selection switch. The method comprises an external interrupt routine and a main routine. The external interrupt routine comprises steps: (A) counting the external interrupt signals; (B) checking that the external interrupt signal flag is 1; (C) discriminating that the external interrupt signal is above a certain level; and (D) setting the external interrupt signal flag by 1. The main routine includes: (a) counting the execution time due to the external interrupt; (b) checking the counted value of the instruction execution counter; and (c) discriminating the frequency of AC power.