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can-buscanopen

Canopen auto addressing with LSS, how to architect the system

I am new to Canopen and need to architect a system with the following characteristics:

  • 1 canopen Master (also a gateway)
  • multiple canopen slave nodes, composed by multiple instances of the same device (with unique SNs, as required by LSS)

I would like to design this device to not require any pre-configuration before connecting it to the bus, and also allow devices that were previously connected to another canopen bus (and therefore had a previous node ID) to be seamlessly connected to a new bus (therefore their node IDs should not persist after a reboot). After learning about Canopen and the LSS service I think a good solution would be:

  • The device has no persistent node ID, and at every boot it needs to be addressed by the master through LSS
  • the master will periodically scan and address new nodes through the LSS service (allowing device hot-plug)
  • If for any reason the master reboots, it can re-detect all already addressed nodes through a simple node scan (SDO info upload of all addresses)

Now my questions:

  1. It is not clear to me how to have an "invalid canopen node-ID" (referenced here: https://www.can-cia.org/can-knowledge/canopen/cia305/) when they boot, if it has no initial node ID (and therefore only replies to the LSS addressing service) it should be completely silent on the bus, not even sending a boot-up message when powered (not being canopen compliant) until it gets addressed by the LSS service, but if I give it any default initial node-ID it would cause collisions when multiple nodes are simultaneously powered on (which will be the normal behaviour at every system boot-up, all devices, including the master, will be powered on at the same time), is it valid to have a canopen device "unaddressed" and silent like this, and still be canopen compliant? how to handle this case?
  2. I read that node ID 0 means broadcast, so it means that my master could ask for all (addressed) node infos (through an SDO upload) with just one command (SDO upload info on node ID 0)? or is it not allowed, and I should inquire all 127 addresses on the bus to remap the network?

Thanks

Solution

  • I hope I get your questions because they are bit long:

    Question 1

    Yes, it is CANopen compliant if you have a Node which has no Node-ID. That's what the LS-Service is for. As long as the LSS Master has not assigned a Node-ID to the slave, your are not able to talk to the slave via SDO requests. Also PDO communication is not possible in unconfigured state.

    Question 2

    The ID 0 broadcast is only available for the Master NMT command. That means the CANopen master can set all NMT states of the system at the same time. SDO communication is only available between the Master and one Slave so you have to ask every node individually.