Technical data

Appendix
27.2 Memory Areas of S7 CPUs
Programming with STEP 7
578 Manual, 05/2010, A5E02789666-01
Updating Part Process Images (Process-Image Partitions) with SFCs
You can use SFCs to update the entire process image or a process-image partition from your user
program.
• Requirement: The process image in question is not updated by the system.
• SFC26 UPDAT_PI: Update process-image input table
• SFC27 UPDAT_PO: Update process-image output table.
System Update of the Part Process Images (Process-Image Partitions)
You can also have the system update process-image partitions automatically by calling an OB -
similar to the (entire) process image, which is updated cyclically before or after OB1 is processed.
You can assign this function as a parameter only for specific CPUs.
During operation, the assigned process-image partition is updated automatically:
• Before the OB is processed, the process-image partition for inputs
• After the OB is processed, the process-image partition for the outputs
You assign the parameters for the CPU, along with the priority of the OBs, to indicate which
process-image partition is assigned to which OB.