Xylem CL500 ONLINE CHLORINE ANALYZERS MODBUS - Manual (Page 3)

1.0 Overview
The Global Water CL500 uses a communication protocol called Modbus. A company
called Modicon, for use with their programmable controllers, developed the Modbus
protocol. Since that time Modbus has evolved into common communication protocol in
industry.
The communication method involves using a master-slave technique, in which there is one
master and several slaves. The CL500 is a slave device. Only the master can initiate
queries. These queries are directed to an individual slave device and the appropriate slave
responds with the requested data.
A broadcast message can be sent to all slaves. The slave devices do not answer these
broadcasts.
There are two transmission modes. These modes are known as RTU (Remote Terminal
Unit) and ASCII (American Standard Code for Information Interchange).
The CL500 can be setup in a network of up to 255 slave devices. Each device must have a
different address (1-255). The CL500 can be set for either RTU or ASCII mode.
CL500 Modbus (3/09)
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