Serial comms are at 19200 baud, 8N1
The data is passed in variable length records
Record structure:
  Offset   Usage
    0      start of record (\xda)
    1      Command
    2      direction (\xff PC-> Radio, \x00 Radio -> PC)
    3      length of payload (excluding header/checksum) (n)
    4      payload (n bytes)
    4+n+1  checksum 

 Commands:
   \x80 Start comms/Identify
   \x81 End comms & Reboot
   \x82 Config read
   \x83 Config write
   \x84 Read memory
   \x85 Write memory)