Detcon 880S-N4X User Manual
Page 6
880-N4X
880-N4X Instruction Manual
Rev. 1.0
Page 2 of 40
network, or Modbus™ (Figure 2). RS-485 serial communication is used for multipoint communications and is
a popular choice due to ease of wiring installation.
Advantages of using RS-485 serial communication
:
¾ Inexpensive method allowing multiple devices to communicate over a single twisted pair of wires.
¾ More data/information can be sent beyond the simple 4-20mA signal.
¾ Transceiver communication up to 4,000 feet without using repeaters.
¾ Highly resistant to induced noise when proper cable and terminations are used.
¾ Two-way (bi-directional), half-duplex, data bus communication consisting of multiple transmitter and
receiver combinations.
Most systems use the RS-485 master/slave architecture for multiple device communication. Each slave unit
has a unique address and responds to data packets generated by the master. The master periodically polls all
connected slave units.
The protocol used by Detcon for the RS-485 communications is the Modbus
¥ RTU, which is compatible with
most PLC’s, MMI’s, and distributed control systems. The Modbus
¥ RTU protocol is standard and allows for
a maximum of 32 sensors and/or field devices to be used in this configuration.
ON / OFF
NO COMM
POWER
ALARM 1
ALARM 3
ALARM 2
FAULT
Typical Sensors
1 2
31 32
Figure 2 RS-485 Network Configuration