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If you want to build a ship don't herd people together to collect wood and don't assign them tasks and work, but rather teach them to long for the endless immensity of the sea. (Antoine-Marie-Roger de Saint-Exupéry)

Process Data Objects (PDO)

CANOPEN distinguishes two types of PDOs:

  • Transmit Process Data Objects (TPDOs): PDOs produced by a node;
  • Receive Process Data Objects (RPDOs): PDOs consumed by a node.

In order to use PDOs each node must configure two sets of configuration parameters:

  • communication parameters: indicating which CAN message is used for the PDO and how is it triggered (RPDO / TPDO);
  • mapping parameters: indicating which Object Dictionary entries are contained in the PDO.

For each TPDO and RPDO that are transmitted and received by a node, the Object Dictionary of that node contains one set of configuration parameters called the PDO communication parameters .

Transmission of PDOs is only possible in the Operational state. PDOs have no fixed format. The data field of a PDO can be between one and eight data bytes long. The content of a PDO can also not be readily interpreted. The basic idea here is that both the transmitter and the receiver know how the content of a PDO is to be interpreted. For this reason it is sufficient to identify a PDO only by its COB-ID. The so-called PDO mapping describes which individual process variables in the data field of a PDO are transmitted, how they are arranged and which data type and length they have. Therefore the content and meaning of the data field of each defined PDO is described in the form of a PDO-mapping record inside the object dictionary both on the transmit and on the receive side.