8.5.7. CANopen process data objects
Process data objects (PDOs) are used for the cyclic transmission of (process) data via
CANopen. PDOs only contain data and an identifier. They do not contain any information
about the sender or receiver and are therefore very efficient.
Details
• Process data objects which the inverter receives via the network are referred to as
"Receive PDOs" (RPDOs).
• Process data objects which the inverter sends via the network are referred to as
"Transmit
PDOs" (TPDOs).
• The maximum length of a PDO is 8 bytes (4 data words).
• Each PDO requires a unique identifier ("COB-ID") for the purpose of identification
within
the network.
• Communication parameters such as the transmission type and cycle time for each PDO
can be set freely and independently of the settings of other PDOs
Transmission type
Process data objects can be transmitted in an event-controlled or time-controlled manner.
The below table shows that it is possible to combine the different methods by means of
logic operations (AND, OR):
• Event-controlled: The PDO is sent if a special device-internal event has occurred, for
instance, if the data contents of the TPDO have changed or if a transmission cycle time
has elapsed.
• Synchronous transmission: Transmission of a TPDOs or reception of an RPDO is
effected
after the inverter has received a sync telegram (COB-ID 0x80).
• Cyclic transmission: The cyclic transmission of PDOs is effected when the transmission
cycle time has elapsed.
• Polled via RTR: Transmission of a TPDO is carried out on request by another device via
data
request frame (RTR remote transmit request). For this, the data requester (e.g.
master) sends the data request frame with the COB-ID of the TPDO that is to be
requested to transmit. The receiver recognises the RTR and carries out the
transmission.
different transmission
differcyclic synchronous event-controlled
1 ... 240 • -
Synchronous and acyclic
The PDO is transmitted on an event-controlled basis with every sync (e.g. when a bit change occurs in the PDO).
Synchronous and cyclic (sync-controlled with a response)
Selection n = 1: The PDO is transmitted with every sync.
Selection 1 < n ≤ 240: The PDO is transmitted with every n-th sync.
Asynchronous manufacturer-specific / device profile-specific
If one of these values is entered, the PDO is transferred in an event-controlled or cyclic manner. (The values "254"
and "255" are equivalent).
For a cyclic transmission, a cycle time must be entered for the respective PDO. In this case, cyclic transmission
takes place in addition to event-controlled transmission.
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