Cycle and Response Times of the S7-400
9.8 Interrupt Reaction Time
S7-400 Automation System, CPU Specifications
9-22 Manual, 10/2006, 6ES7498-8AA04-8BA0
9.8 Interrupt Reaction Time
Definition of the Interrupt Response Time
The interrupt response time is the time from when an interrupt signal first occurs to calling
the first instruction in the interrupt OB.
General rule: Interrupts having a higher priority take precedence. This means that the
interrupt response time is increased by the program processing time of the higher priority
interrupt OBs and interrupt OBs with the same priority that have not yet been processed
(queue).
Note
Read and write jobs with the maximum amount of data (approx. 460 bytes), interrupt
response times can be delayed.
When interrupts are transferred between a CPU and DP master, only a diagnostic or
hardware interrupt can be currently reported at any time from a DP chain.
Calculation
Table 9-8 Calculating the Interrupt Response Time
Minimum interrupt response time of the
CPU
+ minimum interrupt response time of the
signal modules
+ DP cycle time on PROFIBUS-DP
_____________________________________
= Shortest response time
Maximum interrupt response time of the CPU
+ maximum interrupt response time of the
signal modules
+ 2 * DP cycle time on PROFIBUS-DP
_____________________________________
= Longest response time
Hardware Interrupt and Diagnostic Interrupt Response Times of CPUs
Table 9-9 Hardware Interrupt and Diagnostic Interrupt Response Times; Maximum Interrupt Response Time Without
Communication
Process interrupt
response times
Diagnostic interrupt
response times
Asynchronous error (OB 85 in
process image update)
CPU
Min. Max. Min. Max.
414 205 µs 218 µs 204 µs 238 µs 164 µs
416 139 µs 147 µs 138 µs 145 µs 107 µs
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