Controller Area Network Bus Protocol¶

CAN Bus Types¶

These are lower level protocols which focus on the Physical and Data Link

CAN Physical Data Frame:

Types:¶

CAN 2.0A: 11bit ID, 8 byte Data, 1 Mbps
CAN 2.0B: 11/29bit ID, 8 byte Data, 1 Mbps
CAN FD: 11/29bit ID, 64 byte Data, 10+ Mbps
CAN XL: 11/29bit ID, 1500+ byte Data, 10+ Mbps

CAN Bus Protocols¶

These are higher level protocol that allow you to use a standard that is heavily adopted by an industry to make the development quicker and easily swapable.

Types: - DeviceNet: Industrial I/O - SAE J1939: Commercial Vehicles - CANOpen: All Applications - CANOpen FD: All Applications

CANopen¶

Extensive Guide: YouTube: CANopen Course - EmSA CANopen

Practical Guide: YouTube: CANOpen Node STM32 From basics to coding

CANOpen is a Higher Layer Protocol (HLP) that is built on top of CAN Protocol to enable a standardisation and advance features over traditional CAN Protocol.

Why is it needed?¶

How do you detect device connectivity (Heartbeat in CANOpen)
How do you figure out configuration change? (Configuration of Frequency in CANOpen)
Standardisation to connect to any device off-market without requiring special configurations.
Supports Device ID (Node ID) which allows P2P Communication (SDO)
Allows One to Many Communication (PDO)
Network Managament: Device Detection, Operational states, reset
Service Access: Point to Point, any data size
Data Access: Multicast, various trigger options
Standard Documentation for various applications like Motors, Drives, etc.

Important Concepts¶

Network Management (NMT)
- Used to execute NMT Services which are used for device initialization, started, monitored or stopped
- Works in Master/Slave Structure with Node being NMT Master.
  - Bootup: Transmitted upon device initialisation to inform other nodes about its existence.
- Master can control operating states of nodes:
  - Request state change
  - Request Reset
Synchronization (SYNC)
Emergency (EMCY) - Emergency: Triggered by the occurrence of CANopen device internal error and are transmitted once for each error
TimeStamp (TIME) (PDO)
Process Data Objects (PDO)
- Real-time data transfer from single node to other nodes
- No protocol overhead
- Max 4 bytes
- Use Case: Transmit/Receive real time value to and from other nodes
- Allows mapping to specific variables in node for automatic transmission or reception of stack
- Can be triggered by Event, Timer, Remote node or Sync Object
(Universal) Service Data Object (SDO)
- Provides access to all params of a object Dictionary
- Used to Request changes/data and response is a confirmation to change or response to a data request.
- Used to change configurations and run diagnostics
- Can be of any parameter size.
- Max 4 byte single request
- Max 7 bytes per segment
- Single Master/Client
- Use Case:
  - Peer to Peer reliable communication
  - Configuring a device at startup
  - Transferring large amount of data with acknowledgement
Node Monitoring (Heartbeat) (SDO)
- Heartbeat: Transmitted cyclically by node. Informs other node about connection status of the current producer node.

CANOpen Initialisation Process on Node

Implementation Link: GitHub: C Implement for CANOpenNode

Data Definition¶

CANOpen uses "Little Endian"
Datatypes:
- Unsignedxx(8,16,24,32)
- Integerxx(8,16,24,32)
- Floating, Time, Strings
- Domain

Node Monitoring (Heartbeat)¶

Heartbeat / Node Guard State Codes

These are the 1-byte values you receive in the data field of a heartbeat message (COB-ID = 0x700 + NodeID):

Hex	Binary	NMT State	Description
`00`	`00000000`	Initializing	Power-on or reset; node not yet booted
`04`	`00000100`	Stopped	Node is stopped (doesn’t process PDOs, only SDO/NMT)
`05`	`00000101`	Operational	Fully active – sends/receives PDO, SDO, SYNC, etc.
`7F`	`01111111`	Boot-Up	Node just booted – waiting for NMT command
`7E`	`01111110`	Pre-Operational	Accepts SDOs, but does not process PDOs or SYNC
`7D`	`01111101`	Unknown (reserved)	Not standard – may indicate vendor-specific state

Object Dictionary: Data Addressing¶

Object dictionary is a look-up table type structure which contains the index and subindex which links to the datatype and the description for the object.
It is predefined during the design of a component and follows ISO Standards. Can be generated using EDS Softwares.
Index: 16 bits, SubIndex: 8 bits which allows upto 24bit addresses for objects.
There are some predefined ranges:
- 1000h - 1fffh: CANOpen Parameters to configure the CANOpen
- 2000h - 5fffh: Manufacturer Specfic data
- 6000h - Afffh: Profile defined data

Process Data Object (PDO)¶

Generally in Producer/Consumer format.
Node is considered as server/producer with the client being considered as consumer.
This is a predetermined table which is used to communicate data at a higher frequency as it allows to club multiple data objects in response/requests and also does not require feedback on successful requests.