A data communication a system including: a stylus including a pen point electrode; a sensor controller; and a host processor. The stylus of data communication system is configured to transmit a pen signal with an electric field by capacitive coupling between the pen point electrode and a sensor electrode group; report, by the sensor controller, a position of the stylus in an operation surface to the host processor in response to detection of the pen signal by the sensor electrode group; supply, by the host processor, data to the sensor controller; and transmit, by the sensor controller, the data to the stylus in a stylus detection period in which the pen signal that is detected by the sensor electrode group indicates that the stylus is present within a predetermined distance from the operation surface.