Question: Trying to use TDM serial port as standard serial port. it is tri-stating when not being driven. Is that supposed to happen?

Answer: When the TDM is used as a standard serial port, it functions the e as the basic standard serial port (see C5x UG, pg 9-23.) When data is not being driven, this port will tri-state and therefore a pull-up must be used to maintain its state.