Object Dictionary; Communication Objects - Sevcon Gen4 Applications Reference Manual

Object Dictionary

Any device connected to the CANopen network is entirely described by its Object Dictionary.
The Object Dictionary defines the interface to a device. You setup, configure and monitor your
Gen4 controller by reading and writing values in its Object Dictionary, using a configuration tool
such as Sevcon's DVT (see page 6-2).
There are two important text files associated with the Object Dictionary. These are:
EDS (electronic data sheet)
An EDS is a text file representation of the Object Dictionary structure only. It contains no data
values. The EDS is used by configuration software such as Sevcon's DVT to describe the
structure of a node's Object Dictionary. An EDS for each Gen4 model and software version, is
available from Sevcon. The EDS file format is described in the DSP306 – Electronic Data Sheet
Specification.
NOTE: Each Object Dictionary matches a particular Gen4 software revision, and its structure is
hard coded into the controller software.
DCF (Device Configuration File)
This is a text file similar to an EDS except that it contains data values as well as the Object
Dictionary structure.
DCFs are used to:

Download a complete pre-defined configuration to a node's Object Dictionary.

Save the current configuration of a node's Object Dictionary for future use.

Communication objects

These are SDO (service data object) and PDO (process data object) as described below. There
is a third object, VPDO (virtual PDO), used by Gen4 which is not a CANopen object. It is
described here because its function is important and similar to that of a PDO.
SDO (Service Data Object)
SDOs allow access to a single entry in the Object Dictionary, specified by index and sub-index.
They use the client–server communication model, where the client accesses the data and the
server owns the target Object Dictionary.
SDOs are typically used for device configuration (e.g. via DVT) or for accessing data at a very
low rate.
PDO (Process Data Object)
PDOs are used by connected nodes (for example in a twin motor configuration) to exchange real
time data during operation. PDOs allow up to 8 bytes of data to be transmitted in one CAN
message.
They use the producer-consumer communication model, where one node (the producer) creates
and transmits the PDO for any connected nodes (consumers) to receive. Transmitted PDOs are
referred to as TPDOs and received PDOs as referred to as RPDOs.
6-4