Tdm Bidirectional Serial Line

I want to implement a two line multiplxer (tx output and rx input) into a single bidirectional line. The checking and control of which path data should take is supposed to be implemented using TIME DIVISION MULTIPLEX TDM. A TDM switch is continously checking if the transmitter buffer has data to transmit and if there is data on the inout line ready to be received. it is suppose to wait here until the eight bits are transmitted on the inout line. when a start bit is detected, on the inout line data is being read into the receiver buffer. Please guys help with a code in VHDL

Your urgent help will be hihly appreciated
Please help guys

Lukas