Siemens SIMATIC NET PROFIBUS Transmission Techniques According to EIA Standard RS-485, Advantages

PROFIBUS NETWORKS

1.2.4Transmission Techniques According to EIA Standard RS-485

EIA Standard RS-485

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:

SThe transmission rate

SThe type of cable being used

Advantages:

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

SPurely 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)

SSimple installation of the bus cable without specialized experience.

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