Technical data

Diagnostics
23.9 Program Measures for Handling Errors
Programming with STEP 7
518 Manual, 05/2010, A5E02789666-01
• To create a data block if the data block for the status information of global data communication
is missing.
The CPU does not change to "STOP" mode when a communication error is detected and OB87 is
not programmed.
You can find detailed information on OBs, SFBs, and SFCs in the corresponding Help on Blocks.
23.9.14 Programming Error (OB121)
Description
The operating system of the CPU calls OB121 when a programming error occurs, for example:
• Addressed timers do not exist.
• A called block is not loaded.
Programming OB121
You must create OB121 as an object in your S7 program using STEP 7. Write the program to be
executed in OB121 in the generated block and download it to the CPU as part of your user
program.
You can use OB121, for example, for the following purposes:
• To evaluate the start information of OB121.
• To enter the cause of an error in a message data block.
If you do not program OB121, the CPU changes to STOP mode when a programming error is
detected.
You can find detailed information on OBs, SFBs, and SFCs in the corresponding Help on Blocks.
23.9.15 I/O Access Error (OB122)
Description
The operating system of the CPU calls OB122 when a STEP 7 instruction accesses an input or
output of a signal module to which no module was assigned at the last warm restart, for example:
• Errors with direct I/O access (module defective or missing)
• Access to an I/O address that is not known to the CPU.
Programming OB122
You must create OB122 as an object in your S7 program using STEP 7. Write the program to be
executed in OB122 in the generated block and download it to the CPU as part of your user
program.