Siemens SIMATIC S7-400 Manual page 149

Increasing the maximum interrupt response time with communication
The maximum interrupt response time increases when communication functions are active.
The increase is calculated with the following equation:
tv = 100 µs + 1000 µs x n%
where n = cycle load from communication
Signal Modules
The hardware interrupt response time of the signal modules is made up as follows:
● Digital input modules:
● Analog input modules:
The diagnostic interrupt response 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.
S7-400 Automation System, CPU Specifications
Manual, 10/2006, 6ES7498-8AA04-8BA0
Hardware interrupt response time = internal interrupt processing time + input delay
You will find the times in the data sheet of the digital input module concerned.
Hardware interrupt response 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.
Cycle and Response Times of the S7-400
9.8 Interrupt Reaction Time
9-23