title: How to use RS485 on beaglebone black
body: <p>I have a beaglebone black with kernel 4.4-ti, I wonder how to use the RS485 on UART4 (P9.11 and P9.13). There is a overlay of 'BB-UART4-RS485' and when I try to load it, it said 'file exists'. </p>
  
  <p>There is the pin P9.27 which is about the DE/RE, should I use it?</p>
  
  <p>I want to connect to a device which has modbus A, mobus B and ground. It is using half duplex.</p>
  
  <p>I try to simply connect the tx and rx on BBB to A and B on the device, there is communication. But the received message is some garbage. </p>
  
  <p>Thanks in advance.</p>