RXD is the interface to the processor's LIN protocol controller or SCI/UART, which reports the state of the LIN bus voltage. LIN recessive (near V_Battery) is represented by a high level on the RXD and LIN dominant (near ground) is represented by a low level on the RXD pin. The RXD output structure is an open-drain output stage. This allows the device to be used with 3.3 V and 5 V I/O microprocessors. If the microprocessor’s RXD pin does not have an integrated pull-up, an external pull-up resistor to the microprocessor I/O supply voltage is required. In standby mode the RXD pin is driven low to indicate a wake-up request from the LIN bus.