Pull-Up And Pull-Down Resistors - ABB C250 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.
C250
V250
32
33
34
35
36
Fig. 2.2 Pull-up and Pull-down Resistors (Four-wire Operation)
Master
Host
Computer
4
Tx+
Tx–
Rx+
Rx–
GND
First Slave
Rx+
32
Rx–
33
Tx+
34
Tx–
35
GND
36
Fig. 2.3 Connecting Multiple Slaves
+5V
1.8kΩ Pull-up
0V
Resistor
'A'
1.8kΩ
Pull-down
+5V
Resistor
1.8kΩ
0V
Pull-up
Resistor 'B'
'A'
1.8kΩ
Pull-down Resistor
0V
C250 / V250
Tx+
Tx-
Rx+
Rx-
GND
Host Computer
'B'
Last Slave
32
Tx+
33
Tx–
34
Rx+
35
Rx–
36
GND
120Ω
Termination Resistor
(External)
Refer to
page 2
Refer to
page 2