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2. Hardware Implementation of the LUFP7 Gateway
2.6.2. Wiring Recommendations for the Profibus-DP Network
• Use a shielded cable with a twisted pair of copper conductors, preferably a type A Profibus-DP cable.
• Connect the reference potentials to one another,
• You may choose the transmission rate, within limits ranging from 9.6 kbit/s to 12 Mbit/s. The choice is made
at network startup and applies to all network subscribers.
• The maximum length of the line (segment) is inversely proportional to the transmission rate.
Transmission rate (bit/s) 9,6 k 19,2 k 93,75 k 187,5 k 500 k 1,5 M 3, 6 or 12 M
Distance/segment (m) 1 200 1 200 1 200 1 000 0 400 200 100
With 3 repeaters 4 800 4 800 4 800 4 000 2 000 800 400
Experience shows that these lengths may be doubled using lines with a section of 0.5 mm².
• Do not connect more than 32 master or slave stations per segment without a repeater, 127 maximum
(repeaters included) with the 3 repeaters; don't use more than 3 repeaters
• Cable routing: keep the bus away from power cables (at least 30 cm), make crossings at right angles if
necessary and connect the cable shielding to the earth on each unit,
• The network ends on an active line termination, at each segment end (see diagram below); many suppliers
have provided their cables with switchable line terminations. The LUFP7 gateway has no internal line
termination and therefore applies a 5V voltage between pins 5 and 6 of its Profibus-DP plug in order to allow
for the use of an external line termination when the gateway is at the end of the line.
D(A)
390 Ω
220 Ω 390 Ω
D(B)GND
+5V
5 3 8 6
Active line
termination
recommended
at both ends
N.B. if you use a 490 NAD 911 03 connector on each of the two stations located at segment end, you won't
have to use an external line termination, since a line termination is integrated to that type of connector.
However, if you must disconnect a station to which such a connector is connected, move the connector to
another station on the same network so that the line termination continues to be supplied. If you do not wish
to make that type of arrangement, preferably use connectors featuring a switchable line termination.