This is used in protocols such as Bluetooth.Bisync differs from protocols that succeeded it in the complexity of message framing. The syndrome is initialised to 0xFFFF at the start. The application layer data with CRC should then be encoded to the hex string form.Ī CRC-16-CCITT checksum is used, defined by the polynomial x 16+x 12+x 5+1, or 0x1021. The result is 2 bytes, which are appended to the application layer data as the high then the low byte. The Start (STX) and End (ETX) bytes are excluded from the CRC calculation. The CRC is calculated over all bytes from the application layer before the hex string encoding. The CRC bytes allow the integrity of the message to be checked. With more than 100 ms between bytes, the module will discard the in-progress receive operation and wait for the next start byte. Within a single message, bytes should not be spaced by more than 100ms. There are 2 exceptions: the configuration save request (CFG_SR) and configuration factor reset (CFG_FR) may take up to 1.5 sec to reply.Ī 100ms inter-byte timeout is implemented on the module to recover from incomplete requests. The application protocol uses a request/answer mechanism, where all requests are initiated by the asset.
The last row of the table shows the bytes sent over the serial link. This is encoded to 0x34 (‘4’) and 0x38 (‘8’), So our example array becomes: H Take the first character H above, which is 0x48. This hex data is encoded as high and low nibbles. We will work with our data as bytes or collections of bytes with a value 0x00 to 0xFF. We will work in the hex notation.įor example, the ASCII string Hello World! can be represented as a hex array 0x48 0圆5 0圆C 0圆C 0圆F 0x20 0x57 0圆F 0x72 0圆C 0圆4 0x21. This can be illustrated with some examples.įirst, consider that the same data can have a variety of representations.
This means a single byte is sent as 2 characters in ASCII, in the order high nibble then low nibble. The protocol data and CRC data are encoded as hex strings. This implies that the reception of STX or ETX has an unambiguous meaning – they always indicate the start or end of a message. The transport layer protocol is encapsulated by Start of Transmission (STX = 0x02) and End of Transmission (ETX = 0x03) characters.Īll other characters at the transport layer will be printable ASCII characters in the range ‘0’-‘9’ and ‘A’-F’. Transport Layer Description Message Structure #