Device Architecture

Device Architecture

The architecture of a CANopen device is standardized and shown in the following figure:

The central component in a CANopen device is the "Object Directory (OD)". The OD is organized as a table with object entries. Each "Entry" is addressed with a unique combination of "Index" and "SubIdx". The index is a 16 bit value (from 0 ... 0xFFFF), and the sub-index is a 8 bit value (from 0 ... 0xFF). Within the CANopen standard, the layout and usage of many object entries is specified and marked as "mandatory", "optional" or "manufacturer specific". The following table shows an overview of the OD areas:

The "Communication Unit (CU)" uses the OD to set and get configuration settings, inform the device application about new received process data and transmit the device process data to the CAN network. For the different requirements of these activities, different CANopen protocol elements are specified. The CU takes care of all necessary operations to be compliant with the CANopen standard. The following table shows an overview of the UC modules and their responsibility:

The "Network Management State Machine (NMT)" of all CANopen devices within a CANopen network is controlled by the CANopen network master. The following state machine is specified:

Within this state machine, the state transitions with a number (e.g. [129]) will be activated with a network management command equal to this number. If no transition criteria is stated, the transition will be activated after finished state operations automatically. The following table summarizes the network management commands:

These NMT commands used by the CANopen network boot-up master to control the network. During the different states, the listed communication services are allowed:

Note: The Boot-Up message is sent only once during the transition from "Initialization" to "Pre-Operational".