Pull-Up And Pull-Down Resistors; Termination Resistor - ABB COMMANDER 500 User Manual

...2 ELECTRICAL INSTALLATION
2.4 Pull-up and Pull-down Resistors – Figs. 2.1 and 2.2
To prevent false triggering of slaves when the master (host computer) is inactive, pull-up and pull-
down resistors must be fitted to the RS422/485 interface in the host computer – see Figs. 2.1 and 2.2.
Fig. 2.2 Pull-up and Pull-down Resistors (Four-wire Operation)
2.5 Termination Resistor – Fig. 2.3
For long transmission lines, a 120Ω termination resistor must be fitted to the last slave in the chain
– see Fig. 2.3.
Master
Computer
4
C500
Tx+
32
Tx–
33
Rx+
34
Rx–
35
C
36
Rx+
Rx–
Host
Tx+
Tx–
GND
Fig. 2.3 Connecting Multiple Slaves
+5V
1.8kΩ Pull-up
0V
Resistor
+5V
1.8kΩ
Pull-up
Resistor
1.8kΩ
Pull-down Resistor
0V
C500
First Slave
Tx+
32
Tx-
33
Rx+
34
Rx-
35
C
36
Host Computer
'B
'A
1.8kΩ
Pull-down
Resistor
0V
'B
'A
Last Slave
32 Tx+
33 Tx–
34 Rx+
35 Rx–
36
C
120Ω

Termination Resistor

(External)