TXD is the interface to the node processor LIN protocol controller 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_SUP). See Figure 8-3. The TXD input structure is compatible with processors with 3.3 V and 5 V logic I/O. TXD has an internal pull-up resistor to an internal voltage rail that either matches the processor I/O voltage rail or the LDO output rail, V_CC which is determined by the state of pin 7 at power up. The LIN bus is protected from being stuck dominant through a system failure driving TXD low through the dominant state timeout timer. The TXD pin is also used to help determine what mode to enter in pin control mode.