A method in which a sensor controller is connected to a sensor having an electrode group provided together with a display panel configured to operate in during a variable refresh cycle among a plurality of refresh cycles, and an active stylus performs bidirectional communication with the sensor controller. According to the method, the sensor controller acquires a present refresh cycle among the plurality of refresh cycles of the display panel, generates an uplink signal, which serves as a reference for synchronization corresponding to the acquired present refresh cycle, and transmits the uplink signal to the active stylus, which is not detected as yet or is detected already, at the present refresh cycle.