CAN Newsletter magazine
In the CiA 1301 CANopen FD application layer specification, the device type identification of multi-logical devices has been simplified and the EMCY protocol supports the logical device approach.
Logical devices are not new in CANopen technology. They have been introduced already in the beginning, in the mid of the 90ties. The idea is simple: The object dictionary address range for profiles standardized by CiA, 6000h to 9FFFh, is divided in eight parts of 800h 16-bit indexes. For most of the CiA profiles this is sufficient, so that multiple profiles of the same kind or of different functionality can be implemented. For example, the CANopen device can host up to eight CiA 402 drive profiles meaning one CANopen interface is responsible for up to eight motion controllers. Another example is the combination of one CiA 401 (generic I/O) device and one dedicated CiA 420 profile for extruder downstream devices. This functionality is perhaps underestimated. Multiple logical devices can be used to hide sub-layered deeply embedded networks representing up to eight functions. This could also be used as migration path for proprietary sub-networks.
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