Simpler code than bit banging to get multiple serial hardware working with 8051
the TXD line goes from low to high when it signals data is ready. and
  it makes me think TXD will stay low if no data is transmitted.


According to the Atmel 8051 Microcontrollers Hardware Manual TXD idles high. This is consistent with going from low to high when the data bit is 'ready' to be clocked into the receiver.