MODBUS Communication protocol manual

Coolmay PLC Modbus Communication Protocol Manual

1.Introduction

Modbus Communication protocol has been widely used in various fields,as standard industrial

communication protocol. Coolmay PLC RS485 communication interface supports this kind

communication protocol so that PLC can communicate with device with MODBUS communication

protocol conveniently, such as converter, temperature module, humidity module, configuration

network, and various sensors etc.

The Modbus communication protocol is divided into two series communication modes, ASCII

and RTU. When configuring each PLC, User choose communication mode and RS485 serial port

communication parameters (Baud rate, parity check etc), all devices on the Modbus bus should have

same communication mode and series communication parameters. Using Modbus

communication,the relevant special components of each PLC must be set in the ladder diagram.

Coolmay PLC is with default programming port(RS232/RS422), besides, two communication

port (RS232/RS485)is optional installed to meet users’ external connection to three types equipment.

★

RS232/RS422

（

PLC Programming port protocol

）：

Support Mitsubishi programming port

protocol.

★

RS485

（

A[485+] B[485-] Port

）

/RS232

：

Support Mitsubishi programming port protocol,

Mitsubishi serial port protocol and MODBUS protocol (Modbus RTU/ASCII Protocol

communication parameters is set in D8120,Station number is set in D8121,and could be used as

master or slave.)

◆

Could be special customized as 2 way RS485, support Modbus Protocol Master.

Second RS485 COM Port(A1 B1) is used as MODBUS master communication function.

1,Set communication parameter in D8160 so that PLC ladder diagram runs under the condition of

MODBUS master communication. When M8161 is “ON”,RD3A and WR3A instructions are

switched to communicate with the second RS485 communication port (A1,B1).