Pull-Up And Pull-Down Resistors; Termination Resistor; Serial Connections - ABB SM3000 User Manual

SM3000
Multipoint Videographic Recorder

7.5.3 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 must be
fitted to the RS422/485 interface in the host computer.
Resistors are normally connected to the interface by means of
hard-wired links or switches – refer to the manufacturer's
instructions

7.5.4 Termination Resistor

For long transmission lines, a 120  termination resistor must
be fitted to the last slave in the chain – see Fig. 7.9.
Master
First Slave
Last Slave
120W
Termination Resistor
Fig. 7.9 Connecting Multiple Slaves
IM/SM3000–EN Rev. L
Host
Computer
20 19 18 17 16
20 19 18 17 16

7.5.5 Serial Connections

Connections to the Modbus serial board must be made as
shown in Fig. 7.8. Connections to two-wire or four-wire link
configurations on systems with multiple slaves must be made in
parallel as shown in Fig. 7.9. When connecting cable screens,
ensure that 'ground loops' are not introduced.
The maximum serial data transmission line length for both
RS422 and RS485 systems is 1200 m. The types of cable that
can be used are determined by the total line length:
– standard screened or twisted pair cable.
Up to 6 m
– twin twisted pair with overall foil screen and
Up to 300 m
an integral drain wire.
– twin twisted pair with separate foil screens
Up to 1.2 km
and integral drain wires.
7 Installation
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