Siemens SIMATIC S7-1500 warning OB82: Diagnostic interrupt
The operating system calls OB82 when a diagnostics-capable module detects a change in its diagnostic status (incoming or outgoing), when a power supply or battery backup error occurs, and when it detects memory errors. On the S7-1500 the default reaction if OB82 is not configured is to ignore the event: the CPU stays in RUN and the event is entered in the diagnostics buffer. On S7-300/400, a missing OB82 puts the CPU in STOP.
Diagnose this with AI
Try Free PLC Fault Diagnostic Upload a keypad photo, the fault history or a parameter export from your Siemens SIMATIC S7-1500. InduQT compares the evidence and suggests the next useful checks.
When it happens
- RUN, when a module channel reports a fault such as wire break or short circuit (if enabled)
- Any time a power supply or battery backup error is detected
Likely causes and checks
1Channel fault on an I/O module (wire break, short circuit, missing load voltage)
- Points to it
- ERROR LED on the module; OB82 start information names the hardware identifier (LADDR) and Channel.
- Check
- Open the module in Online & diagnostics and read the channel diagnostics; check the field wiring and load supply.
2Power supply or battery backup error
- Points to it
- Diagnostics buffer entry for the supply; occurs with supply events.
- Check
- Check the system and load power supplies feeding the CPU and modules.
3Diagnostics enabled on unused channels
- Points to it
- Repeated incoming/outgoing diagnostics from channels with nothing connected.
- Check
- Compare the module diagnostic settings with the channels actually wired.
Telling it apart
- OB82 is a diagnostic status change on a module that is still there; a module that is removed or not responding calls OB83, and a whole station or IO system failure calls OB86.
- IO_state bit 15 separates a network error (0) from a hardware error (1) when the error or not-available bit is set.
Evidence to collect
- Diagnostics buffer export
- Online & diagnostics view of the module and channel
- OB82 start information (IO_state, LADDR, Channel, MultiError)
- Module diagnostic settings from the project
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