Cycle and Reaction times
3-2
PLC S7-300, CPU Specifications CPU 312 IFM to CPU 318-2 DP
A5E00111190-01
3.1 Cycle time
Cycle Time – A Definition
The cycle time is the time that elapses during one program cycle.
Component Parts of the Cycle Time
The cycle time comprises:
Factors Remarks
Operating system execution time
Process image transfer time
(PII and PIO)
See Section 3.2
User program execution time Can be calculated on the basis of the execution times of the
individual instructions (see the S7-300 Instruction List ) and a
CPU-specific factor (see Table 3-3)
S7 timer (not in the case of the
CPU318-2)
PROFIBUS DP
See Section 3.2
Integrated functions
Communication via the MPI You configure the maximum permissible cycle load produced by
communication in percent in STEP 7
Loading through interrupts See Sections 3.4 and 3.5
Figure 3-1 shows the component parts of the cycle time
PII
Operating
system
User
program
PIO
Interrupts
Operating
system
User
program
Figure 3-1 Component Parts of the Cycle Time
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