2-3
Section
Setting up a PROFIBUS-DP network
19
At baud rates over 1.5 Mbit/s, always use
special PROFIBUS-DP connectors with
built-in series inductances, to ensure that
cable
reflections
caused
by
the
capacitive load of each unit are
minimised.
Connectors with built-in inductors and
termination resistors, as shown here, are
available from various manufacturers
.
PROFIBUS-DP Connector with
built-in inductors and
termination
PROFIBUS-DP Connector
Pin No. Signal
Description
1
Shield Shield / protective ground
2
–
–
3
B-line
Data signal
4
RTS
Direction control signal for repeaters (TTL)
5
DGND Data ground for terminator resistance (0 Vdc)
6
VP
Supply voltage for terminator resistance (+5Vdc)
7
–
–
8
A-line
Data signal
9
–
–
Case
Shield Protective ground
The signal RTS (TTL signal relative to DGND) is meant for the direction control
of repeaters in case repeaters without self control capability are used.
The signals VP and DGND are meant to power
an externally mounted bus terminator (see
figure). The powering of the 220
Ω
termination
resistor ensures a defined idle state potential
on the data lines. To ensure proper functioning
up to the highest baud rate, the bus cable has
to be terminated at both ends of the cable.
PROFIBUS-DP Termination
To ensure electro-magnetic compatibility (EMC), the shield of the cable should
be connected to the metal case and to pin 1 of the connector.
If the Unit is installed within a control cabinet, the cable shield of the incoming
bus cable should be electrically connected to a grounding rail as close as
possible to the cable lead-through using a shield grounding clamp or similar. The
cable shield should continue within the cabinet to the fieldbus device and be
connected there in accordance with the manufacturers instructions.
Ensure that the PLC and the control cabinet in which the device is mounted have
the same ground potential by providing a large-area metallic contact to ground
(use e.g. galvanised steel to ensure a good connection). Grounding rails should
not be attached to painted surfaces.
RTS
VP, DGND
Shielding