Siemens Simatic S7-400 - Manual (Page 136)

Digital Modules
4-14
S7-400, M7-400 Programmable Controllers Module Specifications
A5E00069467-07
Hardware Interrupt
A digital input module can trigger a hardware interrupt for each channel at a rising
or falling edge, or both, of a signal status change.
You perform parameter assignment for each channel separately. It can be modified
at any time (in RUN mode using the user program).
Pending hardware interrupts trigger hardware interrupt processing in the CPU
(OB 40 to OB 47). The CPU interrupts the execution of the user program or of the
priority classes with low priority.
In the user program of the hardware interrupt OB (OB 40 to OB 47) you can specify
how the programmable controller is to respond to an edge change. When the
hardware interrupt OB is exited, the hardware interrupt is acknowledged on the
module.
For each channel the digital input module can buffer an interrupt that has not been
triggered. If no higher priority run-time levels are waiting to be processed, the
buffered interrupts (of all modules) are serviced one after the other by the CPU
according to the order in which they occurred.
Hardware Interrupt Lost
In an interrupt has been buffered for a channel and another interrupt occurs on that
channel before it has been processed by the CPU, a diagnostic interrupt “hardware
interrupt lost” is triggered.
More interrupts on this channel are not acquired until processing of the interrupt
buffered on this channel has been executed.
Interrupt-Triggering Channels
The interrupt-triggering channels are stored in the local data of the hardware
interrupt OBs (in the start information of the corresponding OB). The start
information is two words long (bits 0 to 31). The bit number is the channel number.
Bits 16 to 31 are not assigned.