Pull-Up And Pull-Down Resistors; Termination Resistor; Serial Connections - ABB ScreenMaster RVG200 Operating Instructions Manual

ScreenMaster RVG200
Paperless recorder

3.8.3 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 are fitted to the MODBUS module.

3.8.4 Termination resistor

For long transmission lines, a termination resistor must be fitted to the last slave in the chain – see Fig. 3.11.
Master
Rx/Tx +
Rx/Tx –
Host
COM
Computer
Fig. 3.11 Connecting multiple slaves

3.8.5 Serial Connections

4-wire connections to the MODBUS serial board must be made as shown in Fig. 3.10. Connections to
2-wire systems with multiple slaves must be made in parallel as shown in Fig. 3.9, page 21. When
connecting cable screens, ensure that 'ground loops' are not introduced.
The maximum serial data transmission line length for both RS485 systems is 1200 m (3937 ft.). The types
of cable that can be used are determined by the total line length:
Up to 6 m (20 ft.) – standard screened or twisted pair cable.
Up to 300 m (984 ft.) – twin twisted pair with overall foil screen and an integral drain wire.
Up to 1.2k m (3937 ft.) – twin twisted pair with separate foil screens and integral drain wires.
OI/RVG200-EN
First slave
Rx/Tx +
Rx/Tx –
COM
3 Installation
Last slave
Rx/Tx +
Rx/Tx –
120 
Termination resistor
23