RXD is the interface to the MCU’s LIN protocol controller or SCI and UART, which reports the state of the LIN bus voltage. LIN recessive (near V_SUP) 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 microcontrollers. If the microcontrollers RXD pin does not have an integrated pull-up, an external pull-up resistor to the microcontrollers IO supply voltage is required. In standby mode, the RXD pin is driven low to indicate a wake-up request.