Beckhoff CX8050, Documentation

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CAN
CX8050, CX8051 - Embedded-PCs for
CANopen and CAN 73 Version: 1.4
PDO linking: Peer to Peer
If the consumer-producer model of CANopen PDOs is to be used for direct data exchange between nodes
(without a master), the identifier allocation must be appropriately adapted, so that the TxPDO identifier of the
producer agrees with the RxPDO identifier of the consumer: This procedure is known as PDO linking. It
permits, for example, easy construction of electronic drives in which several slave axes simultaneously listen
to the actual value in the master axis TxPDO.
PDO Communication Types: Outline
CANopen offers a number of possible ways to transmit process data (see also: Notes on PDO
Parameterization [ } 78] ).)
.
Event driven
The ”event" is the alteration of an input value, the data being transmitted immediately after this change. The
event-driven flow can make optimal use of the bus bandwidth, since instead of the whole process image it is
only the changes in it that are transmitted. A short reaction time is achieved at the same time, since when an
input value changes it is not necessary to wait for the next interrogation from a master.
As from CANopen Version 4 it is possible to combine the event driven type of communication with a cyclic
update. Even if an event has not just occurred, event driven TxPDOs are sent after the event timer has
elapsed. If an event does occur, the event timer is reset. For RxPDOs the event timer is used as a watchdog
in order to monitor the arrival of event driven PDOs . If a PDO does not arrive within a set period of time, the
bus node adopts the error state.