TXD is the interface to the processor's LIN protocol controller or SCI/UART that is used to control the state of the LIN output. When TXD is low the LIN output is dominant (near ground). When TXD is high the LIN output is recessive (near V_Battery). See Figure 9-1. The TXD input structure is compatible with microprocessors with 3.3 V and 5 V I/O. TXD has an internal pull-down resistor. The LIN bus is protected from being stuck dominant through a system failure driving TXD low through the dominant state timeout timer.