JVL MAC050 User Manual page 161

4.4 Expansion Modules MAC00-FC2/FC4
4.4.49 PDO (Process Data Object):
PDO: Performs real time transfers, and the transfer of PDOs are 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.
Other PDOs characteristic is, that it doesn't reply when it is receiving data, this for mak-
ing the 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 a RTR connection the Pull model.
Objects are mapped in a PDO. This mapping is an agreement between the sender and
receiver as to 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
to where it should transfer data which it 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
is determined by a corresponding PDO mapping structure within the Device object Dic-
tionary. Number and length of PDOs of a device is application specific and have to be
specified within the device profile
Write PDO service:
The Write PDO service is unacknowledged. There is a PDO producer which sends its
PDO to the PDO consumer. There can be 0 or more consumers in the network. For
receive PDOs, MAC00-FC2/FC4 is the consumer and for Transmit PDOs, the producer.
The following figure shows a Write PDO service:
Read PDO service:
The read PDO service is an acknowledged service. One of the several PDO consumers
send a RTR message to the network. After it has received the RTR message, the PDO
producer sends the requested PDO. This service is used for RTR queries. Using this serv-
ice, an actual value can be interrogated independently of the selected cycle time. The fol-
lowing figure show a read PDO service:
JVL Industri Elektronik A/S - User Manual - Integrated Servo Motors MAC050 - 800
PDO Producer
Request
TT1086GB
PDO Producer
Indication
Response
TT1087GB
0
L = 0....8
Proces data
L = 0....8
0
Proces data
PDO Consumers
Indication
PDO Consumers
Request
Confirmation
157