Siemens Micromaster Profibus - Connecting the Bus Cable via RS485; RS485 Bus Connector Pin Assignment; Maximum Cable Lengths for RS485

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PROFIBUS Optional Board Operating instructions
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A converter can be switched on unintentionally if the serial bus installation is not
operated correctly. The bus must be started up by personnel who are qualified and
trained in installing systems of this type.
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The PROFIBUS optional board has a 9-pin sub D socket for connecting it to the
PROFIBUS system. The terminals are short-circuit-proof and isolated.
Table 4-1 PIN assignment of sub D socket
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1 SHIELD Ground connection
2 - Not assigned
3 RxD/TxD-P Receive/send data P (B/B´) RS-485
4 CNTR-P Control signal TTL
5 DGND PROFIBUS data reference potential (C/C´)
6 VP Supply voltage positive
5 V ± 10 %
7 - Not assigned
8 RxD/TxD-N Receive/send data N (A/A´) RS-485
9 - Not assigned
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RS-485-compliant transmission is the transmission mode used most frequently on
PROFIBUS-DP. This requires a twisted, screened copper cable with one conductor
pair.
A total of 124 devices can be connected to one PROFIBUS line. Up to 32 devices
can be interconnected in a linear structure within one bus segment. If the
configuration includes more than 32 nodes, repeaters (cable amplifiers) must be
installed to link the individual bus segments.
The maximum cable lengths are dependent on the baud rate (transmission speed).
The maximum cable lengths specified in the table below can be guaranteed only
with PROFIBUS bus cables (e.g. Siemens PROFIBUS cable available under order
number (MLFB) 6XV1830-0EH10).
Table 4-2 Permissible cable length of one segment
Baud rate Max. cable lengths of
one segment [m]
9.6 to 187.5 kbaud 1000
500 kbaud 400
1.5 Mbaud 200
3 to 12 Mbaud 100
RS-485 repeaters can be installed to increase the length of a segment.
1
5
6
9
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