Identifier Allocation

Default Identifier

CANopen provides default identifiers for the most important communication objects, and these are derived from the 7-bit node address (the node ID) and a 4-bit function code in accordance with the following scheme:

For broadcast objects the node ID is set to 0. This gives rise to the following default identifiers:

Broadcast objects

Peer-to-peer objects

*) The Beckhoff Default Mapping applies to PDO3 and PDO4. In most configurations, PDOs 3+4 contain data related to analog inputs and outputs, but there can also be "excess" data from digital I/Os, or data from special terminals. Details may be found in the section covering PDO Mapping.

Up until version 3 of the CANopen specification, default identifiers were assigned to 2 PDOs at a time. The BECKHOFF Bus Couplers up to firmware version BA correspond to this issue of the specification. After firmware version C0 (CANopen version 4), default identifiers are provided for up to 4 PDOs.

Manufacture-Specific Default Identifiers for Additional PDOs

Default identifier for additional PDOs

Identifiers are not assigned to the additional PDOs that are filled by the Beckhoff Bus Couplers in accordance with the standard scheme. The user must enter an identifier for these PDOs in the object directory. It is easier to activate the occupied PDOs by means of object 0x5500.

This entry in the object directory extends the default identifier allocation up to 11 PDOs. This creates the following identifiers: