Evaluation Of Hardware Interrupts In The S7-400H System - Siemens SIMATIC S7-400H System Manual

System and operating states of the S7–400H

11.5 Evaluation of hardware interrupts in the S7-400H system

11.5 Evaluation of hardware interrupts in the S7-400H system
When using a hardware interrupt-triggering module in the S7-400H system, it is possible that
the process values which can be read from the hardware interrupt OB by direct access do
not match the process values valid at the time of the interrupt. Evaluate the temporary
variables (start information) in the hardware interrupt OB instead.
When using the process interrupt-triggering module SM 321-7BH00, it is not advisable to
have different responses to rising or falling edges at the same input, because this would
require direct access to the I/O. If you want to respond differently to the two edge changes in
your user program, assign the signal to two inputs from different channel groups and
parameterize one input for the rising edge and the other for the falling edge.
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S7-400H