Description
OB 82 is called by the CPU's operating system whenever

• The diagnostic interrupt has been enabled in a diagnostics-compatible module.
• The diagnostics-compatible module recognizes a change in the diagnostics state.
• The diagnostics-compatible module issues a diagnostics request to the CPU.
• And the CPU is in RUN mode.

If OB 82 is not programmed, the CPU goes into STOP mode.

With DPV1-integration in the S7-300 CPU-DP modules (CPU 31xC / 31x from V2.0.0, CPU 318 2DP from V3.0.0), the processing and acknowledgement of the interrupts in CPU STOP mode is changed in accordance with the DPV1 standard.

When DPV1 is integrated, the diagnostic interrupts are acknowledged when the CPU is in STOP mode and, wherever this is the case, lead to a corresponding entry in the diagnostic buffer.

• This also applies to interrupts that are reported in the STOP mode of the CPU.
• However, no OB82 call occurs because the CPU is in STOP mode.
• A diagnostic interrupt which is received in STOP mode is not executed subsequently if the CPU is in RUN mode again.

Whether or not a slave reports interrupts to the master CPU when it is in STOP mode depends on the slave. Users can ascertain the status of the distributed modules for themselves by outputting relevant system status list IDs (e.g. 0x692) with SFC51.

Note
A description of system function SFC51 is available in the manual in Entry ID: 44240604 or in the Online Help of STEP 7 (select block and press "F1").