PDO

PDOs are messages sent without confirmation used for real-time information transfer. PDOs are mapped to a single CAN frame and can contain multiple object dictionary entries with a maximum of 8 bytes of data. Each PDO has an identifier and is transmitted by only one node in the network, however it could be received by more than one node. PDOs must be configured previous to using them.

There are two types of PDO messages: Transmit PDO (TPDO) and Receive PDO (RPDO).

The trigger event of the PDO message could be configured using the communication parameter object and the object dictionary entries transmitted could be also defined using the PDO mapping list.

Therefore, each PDO is defined by means of:

• A PDO communication parameter
• A PDO mapping object

Controllers based on emcl include 4 RPDO and 4 TPDO.

Transmit PDO (TPDO)

TPDOs are configured to send data from node to master after the occurrence of a trigger event or after a remote request by means of an RTR.

TPDOs have three transmission types:

• Internal event or timer: Message transmission is triggered when the value mapped into the PDO has changed or when the specified time (event-timer) has elapsed. PDO transmission is controlled by producer.
• Remotely request: Message transmission is initiated on receipt of an RTR message. PDO transmission is driven by the PDO consumer.
• Synchronously trigger: Message transmission is triggered by the reception of a certain number of SYNC objects (see TPDO1 definition for further information). The PDO transmission is controlled by the SYNC producer.

Example of an internal event TPDO:

Receive PDO (RPDO)

The master uses the RPDO to write data to objects in the nodes.

RPDOs have two transmission types:

• Asynchronous: Message content is applied upon receipt of the RPDO. The PDO reception is controlled by the PDO producer.
• Synchronously trigger: Message content is applied after the reception of a certain number of SYNC objects. The PDO reception is controlled by the SYNC producer.

Example of an asynchronous RPDO:

Mapping procedure

The steps to configure the PDO mapping are (Example for setting the RPDO 1):

1. Place the controller into NMT pre-operational.
2. Destroy the PDO by writing a 1 into the valid bit of SubIndex 0x01 of PDO communication parameter. (0x1400 RPDO1 - bit 31 of COB-ID used)
3. Unmap all registers from PDO by setting SubIndex 0x00 to zero. (0x1600 RPDO1 mapping parameter).
4. Modify mapping by changing the values in the corresponding SubIndexes. (0x1600 RPDO1 mapping parameter).
5. Enable mapping by setting SubIndex 0x00 to the number of mapped objects. (0x1600 RPDO1 mapping parameter).
6. Create PDO by setting a 0 into the valid bit of SubIndex 0x01 of PDO communication parameter. (0x1400 RPDO1 - bit 31 of COB-ID used)
7. Place the controller into NMT operational.