ControlMaster CM10, CM15, CM30, CM50, CMF160 and CMF310
Universal process controllers and indicator,
1
/8,
1
/4,
1
/2 DIN and fieldmount 5 MODBUS Communications
IM/CM/C–EN Rev. H 17
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.
Fig. 5.3 Connecting Multiple Slaves
Rx+
Rx–
Tx+
Tx–
COM
Host Computer
Tx–
Rx+
Rx–
COM
Tx+
Tx–
Rx+
Rx–
COM
Tx+
Last Slave First Slave
120
Termination
Resistor
Standard
Connections
Standard
Connections
Master
120
Termination
Resistor
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