ABB AC500 PLC Hardware Manual page 1142

Device Specifications
Accessories > AC500-eCo
1.8.1.10.3 Connections
Connection:
Interface
Pin No.
1
2
3
4
5
RS-485 communication requires an electrical termination of the communication line. The fol-
lowing is necessary:
2 resistors of 120 W each at both line ends (to avoid signal reflections)
●
● a pull-up resistor at RxD/TxD-P and a pull-down resistor at RxD/TxD-N. These 2 resistors
care for a defined high level on the bus, while there is no data exchange.
In every RS-485 network 1 pull-up and pull-down resistors must be activated. It is recom-
mended to activate the pull-up and the pull-down resistors at the bus master. These 2 resistors
are integrated inside the TK506 RS-485 isolator. They can be activated by connecting the termi-
nals 1-2 and 3-4 of the terminal block with cable bridges.
Connection: The following figure shows an RS-485 bus with the bus master at the line end.
Modbus Pro-
tocol
Master at the bus line end, pull-up and pull-down activated, bus termination with 120 W
1
resistors
2 Slave within the bus line
Slave at the bus line end, bus termination with 120 W resistors
3
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:
1142
Signal
Terminator P
RxD/TxD-P
RxD/TxD-N
Terminator N
FE
3ADR010121, 13, en_US
Description
Terminator positive
Receive/transmit positive
Receive/transmit negative
Terminator negative
Functional earth (internally
connected to DIN rail spring)
2019/04/17