Device Architecture

Standard Architecture

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

CANopen architecture

Object Dictionary

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:

Index Content
0x0000 Reserved
0x0001 – 0x025F Data types
0x0260 – 0x0FFF Reserved
0x1000 – 0x1FFF Communication profile area
0x2000 – 0x5FFF Manufacturer specific profile area
0x6000 – 0x9FFF Standardized device profile area
0xA000 – 0xBFFF Standardized interface profile area
0xC000 – 0xFFFF Reserved

Communication Unit

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:

CU Module Responsibility
NMT Network Management
SDO Service Data Object Transfer
PDO Process Data Object Transfer
SYNC Synchronization Module
EMCY Emergency Transfer
TIME Time Management

Network Management

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:

NMT States

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:

NMT Command Description
1 Start remote node
2 Stop remote node
128 Enter “Pre-Operational” state
129 Reset node
130 Reset communication

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:

  Init Pre-Op. Operational Stop
Boot-Up Object X      
NMT Object   X X X
SDO Transfer   X X  
SYNC Object   X X  
Time Stamp Object   X X  
Emergency Object   X X  
PDO Transfer     X  

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