Siemens EF 83H Series Manual de usuario descargar pdf (Pagina 24)

Overview

1-8

SIMATIC 505 PROFIBUS-FMS CP User Manual

Network Overview (continued)

PROFIBUS

allows for multiple masters on a single network, where each

master can control the transmission of commands by holding a token. The

token is a special telegram that transfers the right of transmission from one

master to another

. It is circulated among all active masters on a network in

a token ring.

When a network is powered up, each master enters a listening mode, checks

network traffic and builds a list of active stations on the network. This

establishes the token ring for the network. When the first master (lowest

station number) finishes its listening mode, it passes itself the token, and

gains control of the network. Possession of the token indicates the ability to

initiate data transfer

. Before each subsequent token pass, the master

performs a gap update, polling a single sequential station address to see if

another master is waiting to enter the network.

When a second master enters the network, the first master passes it the

token, thereby passing control of the network. In this way

, control of the

network and therefore the ability to issue network commands rotates from

master to master

Figure 1-4 shows an example of token passing among masters on a

PROFIBUS network.

 

Master

Stations

4, 5, and 6 are not part of the token ring

and cannot initiate jobs on the network.



Slave

Slave Slave

Figure 1-4 Token

Passing on a PROFIBUS Network

oken Passing on a

PROFIBUS Network

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Siemens EF 83H Series Manual de usuario Pagina 24