Which organization blocks do you have to load into the CPU to ensure that the CPU does not go into the "STOP" status when a remote I/O fails?
If the CPU recognizes an asynchronous or synchronous error during the cyclical run (e.g. diagnostics alarm of a DP slave or PROFINET I/O device, station failure, etc.), it calls an appropriate organization block (OB). Users thus have the option of responding to this event.
The following OBs have to be loaded in the CPU to ensure that they can be called by the CPU's operating system if an asynchronous or synchronous error occurs.
|OB no.||Explanation||OB called
|82||Diagnostics alarm||A diagnostics-compatible module, for which you have enabled the diagnostics alarm, detects an error and when the error is cleared
(e.g. a short circuit in the input module).
|83||Remove/plug alarm1)||A module in the central or expansion devices is removed and plugged in (e.g. an input module is removed).||Asynchronous error||Yes||Yes|
|- A start event for an Alarm OB is present, but the OB cannot be executed because it has not been loaded into the CPU
- An error has occurred when accessing the instance DB of a system function block.
- An error has occurred when updating the process image (module missing or defective).
|Failure of a DP slave in a PROFIBUS DP master system or of an IO device in the PROFINET IO system.||Asynchronous error||Yes||Yes|
|A programming error has occurred (e.g. called block is not loaded).||Synchronous error||Yes||No|
|An attempt is made to access a non-existent signal module.||Synchronous error||Yes||No|
In the S7-300 CPU, there is a remove/plug alarm only when removing/plugging in modules that are used on the PROFINET IO (e.g. removing an IO device).
If the above-mentioned organization blocks are not loaded in the CPU, the CPU switches to the "STOP" mode after attempting to call them.
If you use the error OBs, then error handling should be programmed for reliable and error-free plant operation or at least a message should be generated in case of an error. Please take into account that the CPU might no longer go into "STOP" and thus dangerous plant statuses might remain unnoticed.
Detailed information on programming the error OBs is available in the STEP 7 Online Help or in the manual "System Software for S7-300/400 System and Standard Functions" in Entry ID: 1214574.
Further information and notes:
The diagnostics buffer of the CPU contains more information and notes about which organization block the CPU has called.
More detailed information on individual error OBs is also available in the STEP 7 Online Help under the following keywords:
- "Diagnostics > Measures in the program for error handling"
- "Calling reference data (LAD/FBD/STL, blocks ...) > Language description, block help, system attributes > Help on OBs"
- "Error OBs"
- "Settings for reporting system errors"
The following entry tells you which organization blocks do you need for error handling in the S7 program of the CPU: 11499205.