Cycle and response times
7.2 Cycle time
Operating system processing time at the scan cycle checkpoint
The operating system processing time at the scan cycle checkpoint is 500 μs. This time is
valid without:
• Testing and commissioning routines, e.g. status/controlling of variables or block status
functions
• Transfer and deletion of blocks, compressing user program memory
• Communication
• Read/write access to the MMC, using SFC82 to 84
Extension of the cycle time due to nested interrupts and due to errors (CPU 315T-2 DP)
Enabled interrupts also extend cycle time. Details are found in the table below.
Table 7-3 Increase in cycle time by nesting interrupts
CPU Process
interrupt
Diagnostic
interrupt
Time-of-day
interrupt
Delay
interrupt
Cyclic
interrupt
CPU 315T-2 DP 500 μs 600 μs 400 μs 300 μs 150 μs
You have to add the program execution time at the interrupt level to this increase.
Table 7-4 Cycle time extension as a result of errors
CPU Programming error I/O access errors
CPU 315T-2 DP 400 μs 400 μs
You have to add the program execution time of the interrupt OB to this increase.
The times required for multiple nested interrupt/error OBs are added accordingly.
S7-300 CPU Data: CPU 315T-2 DP
Manual, 12/2005, A5E00427933-02
7-5
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