Siemens Simatic PCS 7 Commissioning Manual page 18

Process control system foundation fieldbus

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System planning

3.1 Nodes in the FOUNDATION Fieldbus

● Sample calculation

I/O data

The parameters, inputs and outputs of FF devices are distributed over function blocks. An FF

device can have several function blocks. Only configure the required I/O data of an FF device.

The number of processed function blocks has an effect on the macro cycle.

– 15 x 30 ms = 450 ms, corresponds to the cyclic bus time

– reserved bus time for acyclic communication

1050 ms (recommended 70 %), 450 ms (recommended, at least 50 %)

– recommended macro cycle = between 1500 ms and 9000 ms

Commissioning Manual, 03/2013, A5E03880935-02

FOUNDATION Fieldbus

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