code: func (f *Frame) CRC() uint16 {
  	var crc uint16
  	if !f.Header.Protection() {
  		return 0
  	}
  	crcdata := bytes.NewReader(f.buf[4:6])
  	binary.Read(crcdata, binary.BigEndian, &crc)
  	return crc
  }
docs: // CRC returns the CRC word stored in this frame