Frequently Asked Question

The COB-ID is not the CAN-ID!
Last Updated 8 months ago


11-bit identifier for CAN data and remote frames as defined in /ISO11898-1/AN. It is at the beginning of every CAN message on the bus. The 11bits identifier consists of 4 bits function code and 7 bits Node-ID.


For example,

Object SYNC has function code 0001b, resulting CAN-ID 000,1000,0000b=080h.

Object TPDO1 has function code 0011b, resulting CAN-ID 001,1000,0000b=180h.

CiA has pre-defined CAN-IDs in the figure below:


According to this standard, you can find the same CAN-ID definition in our CAN manual :


COB-ID: (communication object ID)

identifier that contains the CAN-ID and additional control bits.

The COB-ID sub-parameter in the CANopen dictionary is a 32-bit value. It contains some control bits, e.g. bit 29 indicating how to interpret following bits. In case bit 29 is 0, the following 18 bits are ignored and the remaining 11 bits are regarded as the CAN-ID to be used for the PDO. It is transmitted using the CAN base frame format. If the bit is 1, the following bits are interpreted as a 29-bit ID. This means the corresponding PDO is transmitted in the CAN extended frame format.

Bit 30 is used to indicate if CAN remote frames are allowed or not. This is not supported by all CAN implementations. In some, the remote frame transmission can't be disabled.

Bit 31 enables and disables the PDO transmission respectively the reception function. This means you can switch-off the PDO transmission. The reception of CAN messages can’t be switched-off, but the CANopen protocol stack doesn’t process the received PDO when you have disabled it.

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