Goodrive20-UL Series VFD
Communication protocol
-113-
Chapter 7 Communication protocol
7.1 Modbus protocol introduction
Modbus protocol is a software protocol and common language which is applied in the
electrical controller. With this protocol, the controller can communicate with other devices via
network (the channel of signal transmission or the physical layer, such as RS485). And with
this industrial standard, the controlling devices of different manufacturers can be connected to
an industrial network for the convenient of being monitored.
There are two transmission modes for Modbus protocol: ASCII mode and RTU (Remote
Terminal Units) mode. On one Modbus network, all devices should select same transmission
mode and their basic parameters, such as baud rate, digital bit, check bit, and stopping bit
should have no difference.
Modbus network is a controlling network with single-master and multiple slaves, which means
that there is only one device performs as the master and the others are the slaves on one
Modbus network. 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 ensure there is only one slave sends message to the master at a time for the avoidance
of singles impact.
Generally, the user can set PC, PLC, IPC and HMI as the masters to realize central control.
Setting certain device as the master is a promise other than setting by a bottom or a switch or
the device has a special message format. For example, when the upper monitor is running, if
the operator clicks sending command bottom, the upper monitor can send command message
actively even it can not receive the message from other devices. In this case, the upper
monitor is the master. And if the designer makes the VFD send the data only after receiving
the command, then the VFD is the slave.
The master can communicate with any single slave or with all slaves. For the single-visiting
command, the slave should feedback a response message; for the broadcasting message
from the master, the slave does not need to feedback the response message.
7.2 Application
The Modbus protocol of the VFD is RTU mode and the physical layer is 2-wire RS485.
7.2.1 2-wire RS485
The interface of 2-wire RS485 works on semiduplex and its data signal applies differential
transmission which is called balance transmission, too. It uses twisted pairs, one of which is
Summary of Contents for GD20-0R4G-2-UL
Page 1: ......
