TXD is the interface to the MCU LIN protocol controller or SCI and UART that is used to control the state of the LIN output. When TXD is low the LIN output is dominant (near ground) and when TXD is high the LIN output is recessive (near V_SUP), see Figure 9-1.

The TXD input structure is compatible with 3.3 V and 5 V microcontrollers and integrates a weak pull-down resistor. The LIN bus is protected from being stuck dominant through a system failure driving TXD low through the dominant state timer-out timer. When a change of state on the WAKE pin initiates a local wake-up event, the TXD pin is pulled hard to ground indicating a local wake-up event. The hard pull to ground is released upon the rising edge on the EN pin. If an external pull-up resistor is added to the TXD pin to the microcontollers IO voltage then TXD is pulled high to indicate a remote wake-up event.