CAN Communication
CANopen Application Layer
EPOS4 Communication Guide
3-30 CCMC | 2019-11 | rel8759
3.3.3.3 SYNC Object
The SYNC producer provides the synchronization signal for the SYNC consumer.
As the SYNC consumers receive the signal, they will commence carrying out their synchronous tasks. In
general, fixing of the transmission time of synchronous PDO messages coupled with the periodicity of the
SYNC Object’s transmission guarantees that sensors may arrange sampling of process variables and that
actuators may apply their actuation in a coordinated manner. The identifier of the SYNC Object is available
at index “1005h”.
Figure 3-18 CAN communication – Synchronization object (SYNC)
Synchronous transmission of a PDO means that the transmission is fixed in time with respect to the trans-
mission of the SYNC Object. The synchronous PDO is transmitted within a given time window “synchronous
window length” with respect to the SYNC transmission and, at the most, once for every period of the SYNC.
The time period between SYNC objects is specified by the parameter “communication cycle period”.
CANopen distinguishes the following transmission modes:
• synchronous transmission
• asynchronous transmission
Synchronous PDOs are transmitted within the synchronous window after the SYNC object. The priority of
synchronous PDOs is higher than the priority of asynchronous PDOs.
Asynchronous PDOs and SDOs can be transmitted at every time with respect to their priority. Hence, they
may also be transmitted within the synchronous window.
Figure 3-19 CAN communication – Synchronous PDO
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