* Add RS485 echo test for our EMC verification.
* The test is more flexible than the legacy RS485 ping pong test and will
  always recover from transmission errors due to EMI.
* The sent data includes a hard-coded 4-byte header and a 4-byte data length
  field, which is parsed by the receiver. The receiver always scans the
  received data for the header bytes in order to detect a new message.

BCS 746-000125