
6-23
Cabling and Wiring the System
SIMATIC 545/555/575 System Manual
The rules for proper PROFIBUS-DP installation follow:
• Create a daisy-chain arrangement, not a star arrangement. A daisy
chain has two connectors with a single cable (bus wire) connection; all
other connectors (if any) have two cable (bus wires) connections.
• You can connect up to 32 devices on one cable segment. Repeaters count
as devices.
• Do not run the cables near power wires.
• The communication cable consists of two color-coded insulated wires
that are twisted together and surrounded by a shield. The cable is
encased in an insulating jacket. When wiring the system, the same
color of wire must be connected to the TX/RX+ pin throughout the
system.
• Do not cross the TX/RX+ signals and the TX/RX– signals. Wire all of
the TX/RX+ pins (terminal B on the Siemens connectors) together on
each slave device and on the PROFIBUS-DP annex card. Wire all of the
TX/RX– pins (terminal A on the Siemens connectors) together to each
slave device and to the PROFIBUS-DP annex card. Crossing the wires
at any point in the system causes communication problems.
• Proper termination and bias of PROFIBUS-DP cable is important for
reliable communication. The device at each extreme end of a
PROFIBUS-DP cable must be terminated and biased; any connections
made between extreme cable ends must not be terminated or biased.
See pages 6-24 and following for more information about termination
and bias.
• Ground the chassis of each module to earth ground, as described in
Chapter 2.
• All PROFIBUS-DP cable connectors must be properly grounded. With a
Siemens PROFIBUS-DP connector, proper grounding is accomplished
when the bare cable shield contacts the metal connector ground.
• Tighten screws on all PROFIBUS-DP connectors throughout your
system to a maximum torque of 8 in–lb (0.9 N–m) in order to ensure a
good ground connection.
Installing
PROFIBUS-DP Cable
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