A procedure to be performed by a sensor control that periodically transmits an uplink signal and by an input pen that determines a transmission and reception plan for a downlink signal and the uplink signal on the basis of the reception time of the uplink signal. The procedure involves performing an operation of receiving an uplink signal for an initial determinationt time period in accordance with the transmission and reception plan. The procedure involves continuing the operation of receiving an uplink signal for a second period of time instead of transmitting the downlink signal according to the transmission and reception plan by the input pen in response to itthat the uplink signal was not received during the reception operation and the first set time span has expired.
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