Siemens SIMATIC NET PROFIBUS Instrukcja Obsługi Pobierz pdf (Strona 18)

Overview of PROFIBUS DP

DP Base Programming Interface for CP 5613/CP 5614

C79000-G8976-C108-01

2.3 Cyclic Polling by the Master

Polling

Communication between the DP master and the distributed nodes takes the form

of polling. Polling means that the DP master sends cyclic calls to its slaves during

the productive phase. A separate call frame is sent to each DP slave.

In one polling cycle, all the operational DP slaves are addressed. The next polling

cycle starts as soon as the last slave has been addressed. This ensures that the

data is up to date.

DP master

Input data

Output data

DP slaves

Figure 2 Schematic Representation of Polling

Output Data

The call frame contains the current output data that the DP slave will apply to its

output ports. The data belonging to this area are specified by the DP application. If

a DP slave does not have output ports, an "empty frame" is sent to it instead.

Input Data

The reception of a call frame must be confirmed by the DP slave by returning a

confirmation frame. The confirmation frame contains the current input data that are

applied to the input ports of the DP slave. If a DP slave does not have input ports,

an "empty frame" is returned instead.

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Siemens SIMATIC NET PROFIBUS Instrukcja Obsługi Strona 18