Distributed clocks reference clock

The distributed clock unit in the CU112x EtherCAT components is activated by default. The CU112x can therefore be used as distributed clocks (DC) reference clock. The use as DC reference clock is explained below using the example of CU1128.

The EtherCAT reference clock should be located near the start of the system hierarchy, in particular before flexible components (HotConnect). It is therefore advisable to use couplers or junction components such as the CU1128 as DC reference clock.

Without further settings, the TwinCAT System Manager uses the first DC-capable terminal/coupler as the reference clock; see Fig. example topology with EL7201 as reference clock.

Distributed clocks reference clock 1:
example topology with EL7201 as reference clock

If the junction with the EL7201 was uncoupled, e.g. due to topology changes during machine runtime or a fault, the EtherCAT system would lose its reference clock. Central components should therefore deal with this function.

Under Advanced settings for first CU1128 (ESC1), tick the Use as potential Reference Clock checkbox.

Distributed clocks reference clock 2:
activating the CU1128 DC function

Once activated, TwinCAT selects the CU1128 as reference clock.

Distributed clocks reference clock 3:
CU1128 as reference clock

This function can be activated in components, refer here to the notices in the EK1100 documentation.