title: On Board Unit communication via RS485
body: <p>I've heard of On Board Units (OBU) can communicate via RS485.
  My question is, how?</p>
  
  <p>For example, I would like to ask the state of some runtime variables from the OBU (what doors are open?, etc.)
  Or another example, I would like to send some data to the OBU (outside temperature).</p>
  
  <p>What protocol must I implement to do these? Are the any sample implementations available somewhere?</p>
  
  <p>Thanks,
  krisy</p>