Siemens EF 83H Series Instrukcja Użytkownika Pobierz pdf (Strona 23)

Overview

1-7

SIMATIC 505 PROFIBUS-FMS CP User Manual

The

Open Systems Interconnection (OSI) 7 Layer Model defines levels of

communication from the physical layer to the logical layer. While the model

gives functions to the protocols, it does not define the protocols themselves.

PROFIBUS-FMS uses layer 1, layer 2, and layer 7. The OSI 7 Layer Model

is shown in Figure 1-3.

FMS

(Fieldbus Message Specification)

LLI (Lower Layer Interface)

Empty

FDL (Fieldbus Data Link)

RS-485

Application layer

Presentation layer

Session layer

ransport layer

Network layer

Data link layer

Physical layer

The Layers

PROFIBUS-FMS

Figure 1-3 The

OSI 7 Layer Model

Devices on a PROFIBUS network are defined as either masters or slaves.

Masters are able to issue network commands without remote request when

they have the right to access the network. This right is based on the token,

which is discussed below

. Slaves are devices on the network that do not

receive the token, and therefore have no right to issue network commands.

Slaves may only acknowledge received messages, or transmit messages in

response to a master

’

s request.

OSI 7 Layer Model

Masters and Slaves

1 2 ... 18 19 20 21 22 23 24 25 26 27 28 ... 186 187

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