Update Time And Sfb Runtimes - Siemens SIMATIC S7-300 Series Reference Manual

Cycle and Reaction times
PROFIBUS-DP interface
In the case of the CPU 315-2 DP/316-2DP, the cycle time is typically extended by
5% when the PROFIBUS-DP interface is used.
In the case of the CPU 318-2, there is no increase in cycle time when the
PROFIBUS-DP interface is used.
Integrated Functions
With CPU 312-IFM and 314-IFM operation the cycle time increases by a maximum
of 10% when using integrated functions. Also take into consideration a possible
instance DB update during the cycle checkpoint.
Table 3-5 shows the update times of the instance DB at the scan cycle checkpoint,
together with the corresponding SFB runtimes.
Table 3-5

Update Time and SFB Runtimes

CPU 312 IFM/314 IFM
IF Frequency Measurement
(SFB 30)
IF Counting (SFB 29)
IF Counting (Parallel
counter) (SFB 38)
IF Positioning (SFB 39)
Delay of the Inputs and Outputs
You must take account of the following delay times, depending on the module:
S For digital inputs:
S For digital outputs: Negligible delay times
S For relay outputs:
The delay of the relay outputs depends, among other things, on the
temperature and voltage.
S For analog inputs:
S For analog outputs: Response time of the analog output
3-8
Update Time of the
Instance DB at the Scan
Cycle Checkpoint
100 ms
150 ms
100 ms
100 ms
The input delay time
Typical delay times of between 10 ms and 20 ms.
Cycle time of the analog input
PLC S7-300, CPU Specifications CPU 312 IFM to CPU 318-2 DP
SFB Runtime
220 ms
300 ms
230 ms
150 ms
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