Chapter 10 CANopen Function and Operation
Scenario B:
Synchronous mode; ½ synchronization cycle time (for the slave to send data) < = PLC scan time <
synchronication cycle time
A half of the synchronization cycle time is less than a PLC scan time and the PLC scan time is less than or
equals to a whole synchronization cycle time: it is possible that zero PDO will be sent during a
synchronization cycle.
Sync cycle
Sync cycle
Sync cycle Sync cycle
#1
½ Sync ½ Sync
½ Sync ½ Sync
½ Sync
Explanation:
: Once the synchronization cycle starts, the timer starts to count. The counted time should be longer than a
half of the set synchronization time (a rounded-down number) for Master to send PDO to Slave.
: After PLC scan time ends, PLC CPU refreshes to update the synchronization task:
PLC CPU sends PDO and then clears the counted time.
#1: There was no PDO sent from the previous synchronization cycle. Before PLC scan time ends, the next
synchronization cycle comes and the counted time is longer than a half of the set synchronization time (a
rounded-down number), PLC CPU sends PDO and then clears the counted time.
: After PLC scan time ends, PLC CPU refreshes to update the synchronization task:
The counted time of the synchronization cycle is less than half of the synchronization cycle time (for the slave
to send data), the PDO here cannot be sent and the time of the synchronization cycle continues to be counted.
: From the cases in the green section, we know that the time for the PDO to be sent does NOT equal to the
time to perform synchronization, and it is possible that Master can send zero PDO during a synchronization
cycle.
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