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Operation and Maintenance
February 2019
RS485 (serial)
An RS485 connection supports Modbus RTU protocol. Using this connection type, the
Gateway is wired to an RS485 bus which typically leads to a serial I/O card or Modbus I/O
card
(see Figure
manner.
Figure 5-2: RS485 Architecture
A. Engineering station
B. Primary control network
C. Controller and I/O
D. Secondary control network
E. Serial I/O card
F. RS485 bus
G. Wireless Gateway
5.3
Modbus
The Gateway supports both Modbus RTU over the RS-485 serial port and Modbus TCP over
Ethernet. It functions as a sub device on the Modbus network and must be polled by a
Modbus master or client (host system).
36
5-2). Up to 31 Gateways can be connected to a single I/O card in this
Reference Manual
00809-0500-4410
Emerson.com/Rosemount
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