5.7.2 PDO communications
SDO protocol is not the only way to access the object dictionary. PDO allow to transfer data without including their
index and sub-index in the frame. Both are stored in an OD specific field called PDO mapping.
The model used for PDO transmissions also is different. It is a Producer/Consumer model in which data are sent by a
producer node (TPDO) to a consumer node (RPDO) without any confirmation.
Each PDO is described by a combination of two parameters of the OD: the PDO communication parameters and the
PDO mapping. The PDO communication parameters describe the functioning of the PDO and the PDO mapping
describes its content. eNod4 uses 3 TPDO (2 are programmable) and 5 RPDO.
The PDO transmission mode can be set in the corresponding object with the following attributes:
Synchronous: PDO transmission/reception is triggered by the reception of one or more SYNC messages.
Several options are available :
- cyclic: PDO is sent/received after reception of n (1 n 240) SYNC messages.
- acyclic: PDO is sent at reception of the first SYNC message following a specific device event
(activation of a logical input assigned to ‘send TPDO’ or data variation superior to +/- delta)
- on remote transmit request : PDO is sent after the first SYNC message following a remote
transmit request frame with the PDO COB-ID.
Asynchronous: PDO transmission/reception does not depend on the SYNC messages on the CAN bus.
Several options are available :
- on remote transmit request : PDO is sent at reception of a remote transmit request frame with
the PDO COB-ID.
- activation of a logical input assigned to ‘send TPDO’ or data variation superior to +/- delta)
- on a timer event : PDO is sent periodically (with an adjustable period).
The following table recaps the trigger modes that can be chosen by entering the hexadecimal code in the PDO
communication parameter:
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