Moxa Technologies MGate MB3000 Modbus Manuel d'utilisateur télécharger pdf (Page 83)

MGate MB3000 User’s Manual Modbus Overview

A-2

Communication is by Request and Response

All Modbus communication is by request and response. A master sends a request and a slave sends a

response. The master will wait for the slave’s response before sending the next request. For

broadcast commands, no response is expected. This is illustrated by three scenarios as follows:

Normal

The master sends a request to the slave. The slave sends a response with the requested information.

Exception

The master sends a request to the slave. The slave may not support the command or an error is

detected, so it sends an exception to the master.

Broadcast

The master sends a broadcast command, such as a reset command. Every slave on the network

complies with the command, and no response is sent to the master.

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Moxa Technologies MGate MB3000 Modbus Manuel d'utilisateur Page 83