Goodrive10 Series Mini VFD
Communication protocol
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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) 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 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 form 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 mode for 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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