Communication Protocol VD120 Series Inverter User Manual
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Chapter 9 Communication Protocol
VD120 series inverter, providing RS-485 communication interface, using the international standard
Modbus-RTU format communication protocol for the master-slave communication. The user can
realize the centralized control by PC/PLC, controlling the host computer and so on (setting the
frequency inverter control order, the running frequency, the related function code parameter revision,
frequency inverter working condition and fault information monitoring and so on), adapts the specific
application request.
9.1 About Protocol
This Modbus serial communication protocol defines the frame content of asynchronous transmission
information and use format in the series communication and it includes master-polling (or broadcast
address) executive command, data and error checking. The response of slave is the same structure,
and it includes action confirmation, returning the data and error checking etc. If slave takes place the
error while it is receiving the information or cannot finish the action demanded by master, it will send
one fault signal to master as a response.
9.2 Application Methods
VD120 series inverter will be connected into a “Single-master Multi-slave” control net with RS485 bus.
9.3 Bus Structure
(1) Interface mode RS-485 Hardware interface.
(2) Transmission mode
There provide asynchronous series and half-duplex transmission mode. At the same time, just one
can send the data and the other only receives the data between master and slave. In the series
asynchronous communication, the data is sent out frame by frame in the form of message.
(3) Topological mode
In Single-master system, the setup range of slave address is 1 to 247. Zero refers to broadcast
communication address. The address of slave must is exclusive in the network. That is the basis to
guarantee the Modbus serial communication.
9.4 Protocol Description
VD120 series inverter communication protocol is a kind of serial master-slave communication
protocol, in the network, only one equipment (master) can build a protocol, (Named as
“Inquire/Command”). Other equipment (slave) only by providing the data response
“Inquire/Command” or doing the action according to the master’s “Inquiry/Command”. Here, master is
personnel computer (PC), industrial control machine or programmable logical controller(PLC) etc.,
and the slave refers to the VD120 series inverter or other control equipment with the same
communication protocol. Master not only visits some slave, but also sends the broadcast information
to all the slaves. For the single master “Inquiry/Command”, all of slaves will return a signal that is a
response; for the broadcast information provided by master, slave needs not feedback a response to
master machine.
9.5 Communication Frame Structure
VD120 series inverter Modbus protocol communication data format is divided into RTU (remote
terminal unit) mode.
In RTU mode, each byte has the following format:
Encoding system: 8-bit binary, each 8-bit frame field, including two hexadecimal characters,
hexadecimal 0 ~ 9, A ~ F.
Data format: start bit, 8 data bits, parity bit and stop bit. The data format is described in the following
table: In RTU mode, new frames are always started with a transmission time silence of at least 3.5
bytes. In the calculation of the transmission rate to the baud rate on the network, the transmission
time of 3.5 bytes can be easily grasped. Followed by the transmission of data fields are: slave
address, operation command code, data and CRC checksum, each field transfer bytes are
hexadecimal 0... 9, A ... F. The network device always monitors the activity of the communication bus.
Summary of Contents for VD120 Series
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