Beckhoff CX1500-M510 Manual page 97

Product overview
Heartbeat procedure
Protocol
The toggle bit is not used in the heart beat procedure. The nodes send their status cyclically (s). See
Guarding.
2.3.8.2 Process Data Objects (PDO)
Introduction
In many fieldbus systems the entire process image is continuously transferred - usually in a more or less
cyclic manner. CANopen is not limited to this communication principle, since the multi-master bus access
protocol allows CAN to offer other methods. Under CANopen the process data is not transferred in a master/
slave procedure, but follows instead the producer-consumer model. In this model, a bus node transmits its
data, as a producer, on its own accord. This might, for example, be triggered by an event. All the other nodes
listen, and use the identifier to decide whether they are interested in this telegram, and handle it accordingly.
These are the consumers.
The process data in CANopen is divided into segments with a maximum of 8 bytes. These segments are
known as process data objects (PDOs). The PDOs each correspond to a CAN telegram, whose specific CAN
identifier is used to allocate them and to determine their priority. Receive PDOs (RxPDOs) and transmit
PDOs (TxPDOs) are distinguished, the name being chosen from the point of view of the device: an input/
output module sends its input data with TxPDOs and receives its output data in the RxPDOs. This naming
convention is retained in the TwinCAT System Manager.
Communication parameters
Communication parameters
The PDOs can be given different communication parameters according to the requirements of the
application. Like all the CANopen parameters, these are also available in the device's object directory, and
can be accessed by means of the service data objects. The parameters for the receive PDOs are at index
0x1400 (RxPDO1) onwards. There can be up to 512 RxPDOs (ranging up to index 0x15FF). In the same
way, the entries for the transmit PDOs are located from index 0x1800 (TxPDO1) to 0x19FF (TxPDO512).
CX1500-M510, CX1500-B510 Version: 1.0 97