STOBER
9 | Looking for more information about EtherCAT?
02/2020 | ID 443025.06
65
9.5.2.1.2.4
Cycle time < 1 ms
For cycle times < 1 ms, quality defects can occur in the EtherCAT communication if the receipt of the PDO data from the controller and transmission of the process data from the drive
controller overlap. The following graphic shows unstable synchronization using distributed clocks when using TwinCAT 3.
O
I
1
3
2
I
O
I
1
3
2
I
O
I
1
2
O
O
STOBER MC6
Frame
Sync Offset
Shift Time
Data ready
Sync 0
PLL phase offset
AR1
Cycle time
Cycle time
NC+PLC
NC+PLC
NC+PLC
APP
APP
= Jitter
Cycle time
Fig. 15: AS6: DC-Sync – Unstable synchronization, cycle time < 1 ms
In the example, the data transmission (I/O) of the controller is set to task begin in the EtherCAT configuration. For the application cycle sequence, the order is defined as RxPDO, graphical
programming, TxPDO (A149 = 0).