Active pen, sensor controller, and position detection device configured for bidirection communication using time slots

A sensor controller, comprising:

• an interface to a sensor panel, and
• an integrated circuit configured to control operation of the sensor panel to communicate with an active pen by using a series of time slots, to transmit uplink signals to and receive downlink signals from the active pen, wherein the series of time slots are determined based on a reception timing, by the active pen, of one of the uplink signals transmitted from the sensor controller,
• wherein the integrated circuit, in operation,
• receives one of the downlink signals transmitted from the active pen in the series of time slots,
• determines whether or not a gap is included in the downlink signal,
• responsive to a determination that the gap is included, demodulates the downlink signal as a first downlink signal that the active pen transmits by using a time within the series of time slots, and
• responsive to a determination that the gap is not included, demodulates the downlink signal as a second downlink signal that the active pen transmits by using both a time within the series of time slots and a time outside the series of time slots, wherein the second downlink signal is formed by repeating a unit signal that is shorter in duration than each of the series of time slots.