Emerson 1410S Reference Manual page 28

Installing the Gateway
September 2020
3.5.4 RS-485
The Gateway can be ordered with an optional RS-485 (serial) connection (see
Modbus
communicate Modbus RTU on an RS-485 data bus.
Use 18 AWG single twisted shielded pair wiring to connect the Gateway to the RS-485 data
bus. The total bus length should not exceed 4000 ft. (1220 m). Connect the Tx - (negative,
receive) wire to terminal A and the Rx + (positive, transmit) wire to terminal B. The wiring
shield should be trimmed close and insulated from touching the Gateway enclosure or
other terminations.
If the existing data bus uses a 4-wire Full Duplex configuration, see
a 2-wire Half Duplex configuration.
Figure 3-6: Convert from Full to Half Duplex
3.5.5 Shield grounding
The shields of the twisted-pair cables need to be grounded using the grounding terminal
on the Emerson 1410S.
3.5.6 Terminating resistors
Three of the five DIP switches are provided to enable various terminating and biasing
resistors to the RS-485 (Modbus
housing, located in the square opening of the shroud on the upper left side
The switches number left to right going down from 5 to 1. The downward position on the
switch is ON.
Three DIP switches are provided to enable various terminating resistors to the RS-485 data
bus. The terminating resistor on the Emerson 781S connection (120 ohm) is always
enabled.
28
®
terminals are labeled A and B on the wiring diagram. This connection is used to
Tx
Rx
Tx
Rx
®
(A)
) data bus. The switches are found inside the electronics
Reference Manual
00809-0600-4410
Figure
Figure 3-6 to convert to
(B)
(Figure
Emerson.com
3-4).
3-7).