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V2 AC500 Hardware 1-41 System data AC500 / Issued: 05.2007
If the master is located within the bus line, it does not need a terminating resistor. The pull-up and the
pull-down resistors, however, are necessary (see the following drawing).
Slave at the
bus line end,
Master within
the bus line,
Slave within
the bus line
Slave at the
bus line end,
bus termination
120 Ohms
pull-up 470 Ohms
pull-down 470 Ohms
bus termination
120 Ohms
120
Ohms
120
Ohms
5
6
3
6
8
5
1
RxD/TxD-P
RxD/TxD-N
0V
+5V
470
Ohms
470
Ohms
PE
Figure: RS-485 bus, master within the bus line
Attention: If the bus is operated with several masters, the pull-up and pull-down resistors may
only be installed at one master.
The cable shields must be earthed (refer to the chapter "CS31 system bus" of the AC500 system data.
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