What is CANopen?
CANopen is a communication protocol and device profile specification for embedded systems used in automation governed by CiA, a non-profit organisation. The CANopen standard is freely downloadable and consists of an addressing scheme, several small communication protocols and an application layer defined by a device profile.
The communication protocols have support for network management, device monitoring and communication between nodes, including a simple transport layer for message segmentation/desegmentation. The lower level protocol implementing the data link and physical layers is usually a CAN Network.
The basic CANopen device and communication profiles are given in the CiA 301 specification released by CAN in Automation (CiA 301 CANopen application layer specification). More information can be found on the CANopen Wiki.
Every CANopen device has to implement certain standard features in its controlling software.
- A communication unit implements the protocols for messaging with the other nodes in the network.
- Starting and resetting the device is controlled via a state machine. It must contain the states Initialisation, Pre-operational, Operational and Stopped. The transitions between states are made by issuing a network management (NMT) communication object to the device.
- The object dictionary is an array of variables with a 16-bit index. Additionally, each variable can have an 8-bit subindex. The variables can be used to configure the device and reflect its environment, i.e. contain measurement data.
- The application part of the device actually performs the desired function of the device, after the state machine is set to the operational state. The application is configured by variables in the object dictionary and the data are sent and received through the communication layer.
Veethree & CANopen
We are experts working with CAN protocols, our in-house Engineering team can work with you to consult and develop your CANopen project.
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