What is PDO and SDO in CANopen?

A Process Data Object (PDO) is used in CANopen for broadcasting the high-priority control and status information, consisting of a single CAN frame and up to 8 bytes of pure application data.

There is a set of parameters in the communication that indicates the CAN Identifier that is used in the PDO and the triggering events that are related to it.

The parameters related to the receiving PDOs are using the index range 1400h - 15FFh, while the transmit PDOs 1800h - 19FFh. The mapping entries that explain the events triggered fall into these ranges - 1600h -17FFh and 1A00h - 1BFFh.

Service Data Object (SDO) is a class that enables access to all entries in a CANopen object dictionary. An SDO consists of two CAN data frames, carrying different CAN Identifiers, making a confirmed communication service.

With the SDO, devices establish a peer-to-peer client-server communication on the broadcast CAN medium, where the owner of the accessed object dictionary acts like the server of the SDO communication, while the other device is the SDO client.

There are three variants supported from a CANopen device for the SDO protocol:

• Expedited transfer
• Normal (segmented) transfer
• Block transfer

What type of SDO will be used is indicated by the client device during the initiation.