Siemens SIMATIC Manual page 299

The program acknowledges the diagnostic interrupt at the module when it exits OB40.
Note
Note: the system does not generate a hardware interrupt if your limit setting exceeds the
overshoot or undershoot range.
Structure of the start information variable OB40_POINT_ADDR of OB 40
The channel at which a specific limit is exceeded is logged to the OB40_POINT_ADDR
variable in the start information of OB40. The diagram below shows the bit assignment of
DWORD 8 in local data.
Figure 5-7
Hardware interrupt triggered by "End of cycle reached"
You can synchronize a process with the cycle of the analog input module by programming a
hardware interrupt trigger at the end of the cycle.
One cycle comprises the conversion of the measured values of all active channels of the
analog input module. The module processes the channels in successive order. After all
measured values were successfully converted, the module outputs an interrupt to the CPU in
order to report new measured values at its channels.
You can always use this interrupt to download the actual converted analog values.
S7-300 Module data
Manual, 06/2017, A5E00105505-AJ
Start information of OB40: which limits event has triggered a hardware interrupt
Principles of analog modules
5.9 Interrupts of analog modules
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