Writing of persistent data: System behaviour

Write trigger

Internal optimization of persistent data access

Persistent data consistency

Plc cycle time exceedance

Function block  WritePersistentData

None

All data is from same plc cycle.

Yes, if writing of all data takes more than plc cycle time.

Function block FB_WritePersistentData and SPDM_2PASS

Yes

All data is from same plc cycle.

Yes, if writing of all data takes more than plc cycle time.

Function block FB_WritePersistentData and SPDM_VAR_BOOST

Yes

The data of each variable is from same plc cycle.

Rare, if writing of biggest pers. variable takes more than plc cycle time.

TwinCAT system stop (all persistent data is written automatically on TwinCAT system stop).

Yes

All data is from same plc cycle.

None