Technical data

2.3 Network Topology
2.3.1 Topology of an Electrical SINEC L2 Network for
the RS-485 Technique
In an electrical SINEC L2 network, the bus cable is a shielded, twisted pair
(SINEC L2 bus cable). The characteristic impedance is 160 ohms. All the
stations are connected to the SINEC L2 bus cable using SINEC L2 bus
terminals. Each SINEC L2 bus segment must be terminated at both ends.
This line terminator is integrated in each bus terminal and is connected in
the two bus terminals at the end of the cable.
Fig. 2.5 illustrates the typical structure of a SINEC L2 network for RS-485.
The SINEC L2 topology is a linear bus. By using the SINEC L2 repeater,
several SINEC L2 bus segments can be connected together extending the
SINEC L2 bus system length and increasing the number of stations.
RS-485 allows 32 connections (bus terminals or repeaters) per bus
segment. The maximum length of a segment depends on the data rate
used. The following table (2.1) lists the upper limits for a SINEC L2 bus
cable.
DTE
DTE DTE
DTE DTE
DTEDTE
DTE
R
R
DTE
DTE DTE
Bus segment
Fig. 2.5 Topology of SINEC L2 for RS-485
System Overview B8976060/02
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