Cycle and Reaction times
3-6
PLC S7-300, CPU Specifications CPU 312 IFM to CPU 318-2 DP
A5E00111190-01
Calculation
The (longest) response time consists of the following:
2 Process image transfer time of inputs +
2 Process image transfer time of outputs +
2 Operating system execution time+
2 program execution time+
2 Bus runtime on the PROFIBUS-DP bus system (with CPU 31x-2 DP)
Execution time of the S7 timer+
Delay of the inputs and outputs
This corresponds to the sum of the double cycle time and the delay of the inputs
and outputs plus the double bus runtime.
Operating System Processing Time
Table 3-1 contains all the times needed to calculate the operating system
processing times of the CPUs.
The times listed do not take account of
Test functions, e.g. monitor, modify
Functions: Load block, delete block, compress block
Communication
Table 3-1 Operating System Processing Times of the CPUs
Sequence
CPU
312 IFM
CPU
313
CPU
314
CPU
314 IFM
CPU
315
CPU
315-2 DP
CPU
316-2 DP
CPU
318-2
Cycle control 600 to
1200
ms
540 to
1040
ms
540 to
1040
ms
770 to
1340
ms
390 to
820 ms
500 to
1030 ms
500 to
1030 ms
200 s
Process Image Update
Table 3-2 contains the CPU times for process image updates (Process image
transfer time). The times specified are “ideal values” which are prolonged by
interrupts or by communication of the CPU.
(Process image = PI)
The time required by the CPU time for a process image update is calculated by
K + number of bytes in the PI of module rack “0”A
+ number of bytes in the PI of module racks “1 to 3“B
+ number of bytes in the PI via DP D
= Process image transfer time
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