Goodrive30 Series VFD Communication protocol
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7 Communication protocol
7.1 Brief instruction to Modbus protocol
Modbus protocol is a software protocol and common language which is applied in the
electronic controller. With this protocol, the controller (device) 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 send
message to Modbus network for the controlling and inquiring to other devices (slaves). The
slave means the passive device which sends data message to the Modbus network only after
receiving the controlling or inquiring message (command) form 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 computer is running, if
the operator clicks the sending command bottom, the upper computer can send command
message actively even it cannot receive the message from other devices. In this case, the
upper computer 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 of the VFD
The VFD uses the Modbus RTU mode and the physical layer is 2-wire RS485.
7.2.1 2-wire RS485
2-wire RS485 interfaces works in half-duplex mode and send data signals in the differential
transmission way, which is also referred to as balanced transmission. An RS485 interface
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