Hello I am a student studying canopen. What is the relationship between COB-ID and CAN identifier in Canopen? I read on the CIA homepage that COB-ID is not a CAN ID, but I do not understand it.
For example, if a PDO is transmitted over a CAN bus, it will be converted from a CANopen frame to a CAN frame. Will not the CAN identifier be converted using the node ID of the COB-ID? At this time, the COB-ID varies according to the function code, but it is more confusing in that the CAN identifier has only one per device.
To summarize my question, I wonder how CANopen converts identifiers when sending messages via the CAN bus.
Answer
Node ID and COB ID are different things.
Node ID is the hard coded ID of a CANopen device (in the connector).
COB ID is the CAN identifier (11 bits or 29 bits) and the RTR
bit 1: for request, 0: for data
The CAN identifier contains in itself the priority.
In some(?) CANopen standards like CiA-301 some COB-ID ranges or values are reserved.
See: https://en.wikipedia.org/wiki/CAN_bus#Frames
https://www.can-cia.org/standardization/specifications/ CiA-301 V4.2.0 §7.3.5 (to download you need to have a login but it is free of charge)