User's Guide

16

Communication protocol

A message sent must begin with 0x24 0x24 and end with 0x0D 0x0A. In addition, it must contain a size,

8 bits checksum, the message type used and the type of encryption used."

Table 1: example of a simpliﬁed type of message"

In the example on Table 1, byte[1 & 2] are the sync characters which are alway, whether in simpliﬁed or

advanced mode, $$."

byte[3] Length: "

This byte is a computation of the size of the payload the msgType and itself."

byte[4] Msg Type & Encryptio: "

This byte is created by mixing the binary values [MSB 1bits Advanced=1 Simpliﬁed=0][LSB 7 bits

Encryption Type]"

Exemple:

Encryption_Type = 0x01;"

Msg_Type = 0x01;"

byte[4] = Msg_Type<<7 + Encryption_Type;"

##byte[4] = 0x81"

Please see MsgType and Encryption type section for more infos.

byte[n-3] Checksum:

The checksum is calculated over payload using and 8 bits exclusive or (XOR) sequence. It is done prior

to encryption and include payload type. "

byte[n-2] & byte [n-1] Ender:

Each message must be terminated by \r\n (0x0D, 0x0A). This allowes both packet end but also

correlation of length on which if both values are not equals, message is discarded."

sync

length

msg type +

encryption

Payload

type

Data

0x24

0x0F

0x00

0x02

0x41

Data

checksum

Byte termination

0x48

0x45

0x4C

0x4F

0x40

0x0D

0x0A