CAN Protocol

CAN Frames

ASysBus uses extended CAN frames:

Field name	Length (bits)	Purpose
Start-of-frame	1	Denotes the start of frame transmission
Identifier A	11	First part of the (unique) identifier which also represents the message priority
Substitute remote request (SRR)	1	Must be recessive (1)
Identifier extension bit (IDE)	1	Must be recessive (1) for extended frame format with 29-bit identifiers
Identifier B	18	Second part of the (unique) identifier which also represents the message priority
Remote transmission request (RTR)	1	Must be dominant (0) for data frames and recessive (1) for remote request frames
Reserved bits (r1, r0)	2	Reserved bits which must be set dominant (0), but accepted as either dominant or recessive
Data length code (DLC)	4	Number of bytes of data (0–8 bytes)
Data field	0–64 (0-8 bytes)	Data to be transmitted (length dictated by DLC field)
CRC	15	Cyclic redundancy check
CRC delimiter	1	Must be recessive (1)
ACK slot	1	Transmitter sends recessive (1) and any receiver can assert a dominant (0)
ACK delimiter	1	Must be recessive (1)
End-of-frame (EOF)	7	Must be recessive (1)
(Table Source: Wikipedia; CC-BY-SA)

Identifier Encoding

ASysBus uses the Identifier to encode packet type, source and destination. A node address is 11 bit, multicast groups use a 16 bit address. Due to the concept of CAN lower addresses inherit a higher transmission priority.

Packet Types

There are three packet types defined. Please note this definitions differ from the original iSysBus-Protocol.

Unicast

Unicast are sent by a device and addressed to a specific node. These frames are usually only used for management

A0	A1	A2	A3	A4	A5	A6	A7	A8	A9	A10	SSR	IDE	B0	B1	B2	B3	B4	B5	B6	B7	B8	B9	B10	B11	B12	B13	B14	B15	B16	B17
=1	=0	P	O	R	T	!	TA	R	G	E	CAN	CAN	T	A	DD	R	E	S	S	S	O	U	R	C	E	A	DD	RE	S	S

Multicast

Multicast packages are sent to a group of devices. This includes usual control commands like "group light kitchen: light on".

A0	A1	A2	A3	A4	A5	A6	A7	A8	A9	A10	SSR	IDE	B0	B1	B2	B3	B4	B5	B6	B7	B8	B9	B10	B11	B12	B13	B14	B15	B16	B17
=0	=1	M	U	L	T	I	C	A	S	T	CAN	CAN	A	D	D	R	E	S	S	S	O	U	R	C	E	A	DR	E	S	S

Broadcast

Broadcast packages are sent to all devices on the bus. This type is rarely used, example would be "reboot all nodes"

A0	A1	A2	A3	A4	A5	A6	A7	A8	A9	A10	SSR	IDE	B0	B1	B2	B3	B4	B5	B6	B7	B8	B9	B10	B11	B12	B13	B14	B15	B16	B17
=0	=0	B	R	O	A	D	C	A	S	T	CAN	CAN	A	D	D	R	E	S	S	S	O	U	R	C	E	A	DR	E	S	S

Credits

The basic protocol is based on iSysBus