Siemens SIMATIC S7-400 Reference Manual page 113

Increasing the Maximum Interrupt Reaction Time with Communication
The maximum interrupt reaction time increases when communication functions are
active. The increase is calculated with the following formula:
CPU 412:
CPU 414-417:
CPU 41x-4H
where n = cycle load from communication
Signal Modules
The hardware interrupt reaction time of the signal modules is made up as follows:
• Digital input modules
Hardware interrupt reaction time = internal interrupt processing time + input
delay
You will find the times in the data sheet of the digital input module concerned.
• Analog input modules
Hardware interrupt reaction time = internal interrupt processing time +
conversion time
The internal interrupt processing time of the analog input modules is negligible.
The conversion times can be taken from the data sheet of the analog input
module concerned.
The diagnostic interrupt reaction time of the signal modules is the time which
elapses between a diagnostics event being detected by the signal module and the
diagnostic interrupt being triggered by the signal module. This time is so small that
it can be ignored.
Hardware Interrupt Processing
When the hardware interrupt OB 40 is called, the hardware interrupt is processed.
Interrupts with higher priority interrupt hardware interrupt processing, and direct
access to the I/O is made when the instruction is executed. When hardware
interrupt processing is completed, either cyclic program processing is continued or
other interrupt OBs with the same or a lower priority are called and processed.
Automation System S7-400 CPU Specifications
A5E00165965-01
tv = 200 ms + 1000 ms × n%
tv = 100 ms + 1000 ms × n%
tv = 100 ms + 1000 ms × n%, considerable more time possible
Cycle and Reaction Times of the S7-400
3-23