Siemens SIMATIC NET PROFIBUS User Manual

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PROFIBUS Networks SIMATIC NET

6GK1970-5CA20-0AA1 Release 2 05/2000

The RS-485 transmission technique corresponds to balanced data transmission as
specified in the EIA Standard RS-485 /4/.  This transmission technique is
mandatory in the PROFIBUS standard EN 50170 for data transmission on twisted
pair cables.

The medium is a shielded, twisted pair cable.

The bus cable is terminated at both ends with the characteristic impedance. Such
a terminated bus cable is known as a segment.

The attachment of the node to the bus is via a bus terminal with a tap line or a bus
connector (maximum 32 nodes per segment).  The individual segments are
interconnected by repeaters.

The maximum length of a segment depends on the following:

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The transmission rate

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The type of cable being used

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Flexible bus or tree structure with repeaters, bus terminals, and bus connectors
for attaching PROFIBUS nodes

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Purely passive passing on of signals allows nodes to be deactivated without
affecting the network (except for the nodes that supply power to the terminating
resistors)

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Simple installation of the bus cable without specialized experience.