Circuit of frequency counter and method thereof

Abstract

A circuit of frequency counter is adapted for an electromagnetic board with an electromagnetic pen. The counter exemplarily includes a source count module, a motion count module, a logic module, a switching gate module, a signal-capturing module, a frequency-counting module and a control module. The source count module counts number of clock pulses of a first clock signal. A receiver mode is switched by the switching gate module when the number reaches a first predetermined value. The motion count module counts number of clock pulses of a second clock signal. A transmitter mode is made by the switching gate module when the number reaches a second predetermined value. When a cumulative number of circular number counted by the frequency-counting module reaches a third predetermined value, the frequency-counting module completes counting a first high-frequency clock signals, and the control module obtains an operating frequency for the electromagnetic pen.