ABB Advant AC500 Manual page 41

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).
120
Ohms
Slave at the
bus line end,
bus termination
120 Ohms
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.
____________________________________________________________________________________________________________
V2
AC500 Hardware
0V
5
470
Ohms
8
3
6
470
Ohms
6
+5V
Master within
the bus line,
pull-up 470 Ohms
pull-down 470 Ohms
5
RxD/TxD-N
RxD/TxD-P
1
PE
Slave within
the bus line
1-41 System data
120
Ohms
Slave at the
bus line end,
bus termination
120 Ohms
AC500 / Issued: 05.2007