data blocks and retentive memory connection

Retentive memory areas

Data loss after power failure can be avoided by marking certain data as retentive. This data is stored in a retentive memory area. A retentive memory area is an area that retains its content following a warm restart, in other words, after cycling the power when the CPU changes from STOP to RUN.

The following data can be assigned retentivity:

• Bit memory: The precise width of the memory can be defined for bit memory in the PLC tag table or in the assignment list.
• Tags of a function block (FB): You can define individual tags as retentive in the interface of an FB if you have enabled optimized block access. Retentivity settings can be defined only in the assigned instance data block if optimized block access has not been activated for the FB.
• Tags of a global data block: You can define retentivity either for individual or for all tags of a global data block depending on the settings for access.
  • - Block with optimized access: retentivity can be set for each individual tag.
  • - Block with standard access: The retentivity setting applies to all tags of the DB; either all tags are retentive or no tag is retentive.