Communication; Modbus Protocol Introduction; Application To The Vfd - INVT Goodrive18 Series Operation Manual

Goodrive18 series two-in-one VFD

Communication

7 Communication

7.1 Modbus protocol introduction

Modbus is a software protocol, a common language used in electronic controllers. By using
this protocol, a controller can communicate with other devices through transmission lines
(such as RS485). It is a general industrial standard. With this standard, control devices
produced by different manufacturers can be connected to form an industrial network and be
monitored in a centralized way.
The Modbus protocol provides two transmission modes, namely American Standard Code for
Information Interchange (ASCII) and remote terminal units (RTU). On one Modbus network, all
the devices must be consistent in transmission modes, baud rates, data bits, check bits, stop
bits, and other basic parameters.
A Modbus network is a control network with one master and multiple slaves, that is, on one
Modbus network, there is only one device serving as the master, and other devices are the
slaves. The master means the device which has active talking right to sent message to
Modbus network for the controlling and inquiring to other devices. The slave means the
passive device which sends data message to the Modbus network only after receiving the
controlling or inquiring message (command) from the master (response). After the master
sends message, there is a period of time left for the controlled or inquired slaves to response,
which ensures there is only one slave sends message to the master at a time for preventing
signal conflicts.
Generally, you can set the PC, PLC, IPC or HMI as the master to realize centralized control.
Setting a certain device as the master is a convention other than setting by a button or a
switch or the device uses a special message format. For example, if you click the command
sending bottom when the upper monitor is running, the upper monitor can send a command
message actively even it cannot receive the message from other devices. In this case, the
upper monitor is the master. If the VFD is designed to send data only after receiving a
command, the VFD is a slave.
The master can communicate with any single slave or with all slaves. For the single-visiting
command, the slave must send back a response message; for the broadcasting message
from the master, the slave does not need to send back a response message.

7.2 Application to the VFD

The VFD uses the Modbus RTU mode and communicates through the two-wire RS485
network.
Note: The local communication address (P14.00) is set to 1 for group P by default and it is set
to 2 for group F by default. This function code in group P must be different from that in group F.
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