ABB AC500 PLC Hardware Manual page 1281

It is useful, to activate both the pull-up and the pull-down resistors, which only are necessary
once on every bus line, at the bus master.
Pin assignment
Serial
Interface
The following drawing shows an RS-485 bus with the bus master at the line end.
1 Master at the bus line end, pull-up and pull-down activated, bus termination with 120 Ω
resistors
2 Slave within the bus line
3 Slave at the bus line end, bus termination with 120 Ω resistors
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:
2019/04/17
Pin Signal
1 FE
2 TxD
3 RxD/TxD-P
4 RTS
5 SGND
6 +5 V
7 RxD
8 RxD/TxD-N
9 CTS
Shield FE
NOTICE!
Risk of corrosion!
Unused connectors and slots may corrode if XC devices are used in salt-mist
environments.
Protect unused connectors and slots with TA535 protective caps for XC devices
Ä Chapter 1.8.4.6 "TA535 - Protective Caps for XC Devices"
TA535
on page 1172.
3ADR010121, 13, en_US
System Assembly, Construction and Connection
AC500 (Standard) > Connection and Wiring
Interface Description
- Functional earth
RS-232 Transmit data
RS-485 Receive/Transmit
RS-232 Request to send
Signal ground 0 V supply out
- 5 V supply out
RS-232 Receive data
RS-485 Receive/Transmit
RS-232 Clear to send
- Functional earth
Output
Positive
Output
Input
Negative
Input
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