JVL Industri Elektronik A/S - User Manual - Integrated Stepper Motors MIS23x, 34x, 43x 249
10.7 More details of CANopen Theory
10.7.3 PDO (Process Data Object)
PDO: Performs real-time transfers, and the transfer of PDOs is performed without a
protocol. PDOs are used in two ways: for data transmission and for data reception.
PDOs can bundle all objects from the object data directory, and a PDO can handle max
8 bytes of data in the same PDO. The PDO can consist of multiple objects.
Another PDO characteristic is that it does not reply when it is receiving data, in order to
make data transfer fast. It has a high priority identifier.
PDO connections follow the Producer/Consumer model, whereby a normal PDO con-
nection follows the Push model and an RTR connection the Pull model.
Objects are mapped in a PDO. This mapping is an agreement between the sender and
receiver regarding which object is located at which position in the PDO. This means that
the sender knows at which position in the PDO it should write data and the receiver
knows where it should transfer the data to that is received.
The PDOs correspond to entries in the Device Object Dictionary and provide the inter-
face to the application objects. Data type and mapping of application objects into a PDO
are determined by a corresponding PDO mapping structure within the Device object
Dictionary. The number and length of PDOs of a device are application specific and must
be specified within the device profile
Write PDO service:
The Write PDO service is unacknowledged. A PDO producer sends its PDO to the PDO
consumer. There can be 0 or more consumers in the network. For receive PDOs the
MIS23x (SMC75) is the consumer and for Transmit PDOs, the producer.
The following figure shows a Write PDO service:
L = 0....8
PDO Consumer
TT1086GB
Request
Proces data
0
Indication
PDO Producer
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