Pull-Up And Pull-Down Resistors; Termination Resistor - ABB ControlMaster CM10 Manual

ControlMaster CM10, CM15, CM30, CM50, CMF160 and CMF310
Universal process controllers and indicator,

5.4 Pull-up and Pull-down Resistors

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.
Resistors are normally connected to the interface by hard-wired links or switches – refer to the manufacturer's instructions

5.5 Termination Resistor

For long transmission lines, 120 termination resistors must be fitted to the last slave in the chain and the master receive – see
Fig. 5.3.
Tx+
Tx–
Rx+
Rx–
COM
120 
Termination
Resistor
Fig. 5.3 Connecting Multiple Slaves
IM/CM/C–EN Rev. H
1 1
/ ,
8
Last Slave
Standard
Connections
1
/ , / DIN and fieldmount
4 2
First Slave
Tx+
Tx–
Rx+
Rx–
COM
Standard
Connections
5 MODBUS Communications
120 
Termination
Resistor
Rx+
Master
Rx–
Tx+
Tx–
COM
Host Computer
17