Technical data

Diagnostics
23.9 Program Measures for Handling Errors
Programming with STEP 7
510 Manual, 05/2010, A5E02789666-01
23.9.4 I/O Redundancy Error (OB70)
Description
The operating system of a H CPU calls OB70 if a loss of redundancy occurs on the PROFIBUS DP
(for example, if there is a bus failure on the active DP master or an error in the DP slave interface
module) or if the active DP master changes from DP slaves with switched I/Os.
Programming OB70
You must create OB70 as an object in your S7 program using STEP 7. Write the program to be
executed in OB70 in the generated block and download it to the CPU as part of your user program.
You can use OB70, for example, for the following purposes:
• To evaluate the start information of OB70 and determine which event triggered the loss of I/O
redundancy.
• To determine the status of your system using SFC51 RDSYSST (SZLID=B#16#71).
The CPU does not change to STOP mode if an I/O redundancy error occurs and OB70 is not
programmed.
If OB70 is downloaded and the H system is not in redundant mode, OB70 is processed in both
CPUs. The H system remains in redundant mode.
You can find detailed information on OBs, SFBs, and SFCs in the corresponding Help on Blocks.