Open Serial Binary Protocol (SBP) specification

Protocol frame structure

SYNC1	SYNC2	ROUTE	MODE	ID	LENGTH	PAYLOAD	CHECK1	CHECK2
U1	U1	U1	U1	U1	U1	BYTE[LENGTH]	U1	U1
0xBB	0x55	BITFIELD	BITFIELD	1 … 255	0 … 128	BYTEARRAY	0 … 0xFF	0 … 0xFF

Name	Bits	Description
DEV_ADDRESS	0:3 bit	Device address. Default and broadcast address is 0x0.
RESERVED	2 bit	Reserved

Name	Bits	Description
TYPE	0:1 bit	0 — Reserved, 1 — CONTENT: DEVICE → HOST, 2 — SETTING: HOST → DEVICE, 3 —GETTING: HOST → DEVICE
RESERVED	2 bit	Reserved
VERSION	3:5 bit	Field defines the payload data version
MARK	6 bit	Once device is switched on, this flag is always in reset state (ZERO). It can be set to active state (ONE) by the host (see the CMD_MARK command) and the slave device keeps the flag in active state in every frame until hardware reset occurs or is reset by the host. Therefore the host monitors the device's actual settings.
RESPONSE	7 bit	HOST → DEVICE: Set the flag to active state (ONE) in order to get the result of processing the command. The flag doesn't affect the response if one is provided by the TYPE field. DEVICE → HOST: The flag is in reset state (ZERO) by default. Payload goes according to the command specification. If flag is set, the payload contains the result of command processing (see CMD_RESP command).

The checksum algorithm used is the Fletcher-16. Example source code for calculating the checksum:

uint8_t CHECK1 = 0;
uint8_t CHECK2 = 0;
void CheckSumUpdate(uint8_t byte) {
	CHECK1 += byte;
	CHECK2 += CHECK1;
}

Name	Type	Size (Bytes)	Range
S1	int8_t	1	-128 ... 127
U1	uint8_t	1	0 … 255
S2	int16_t	2	-32768 … 32767
U2	uint16_t	2	0 … 65535
S4	int32_t	4	-2'147'483'648 ... 2'147'483'647
U4	uint32_t	4	0 … 4'294'967'295
F4	float	4	-1*2^+127 ... 2^+127
D8	double	8	-1*2^+1023 ... 2^+1023