User`s manual

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.