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 |