Chapter 9 Appendix - Veikong VFD200A Series Operation Manual

Appendix A Modbus communications
The series of inverter provides RS485 communication interface, and adopts MODBUS
communication protocol. User can carry out centralized monitoring through PC/PLC to get operating
requirements. And user can set the running command, modify or read the function codes, the working state
or fault information of frequency inverter by Modbus communication protocol.
A.1 about Protocol
This serial communication protocol defines the transmission information and use format in the series
communication and it includes master-polling (or broadcasting) format, master coding method and the
content includes function code of action, transferring 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.
A.2 Application Methods
The frequency inverter will be connected into a "Single-master Multi-slave" PC/PLC control net with
RS485 bus as the communication slave.
A.3 Bus structure
(1) Hardware interface.
The "485+" and "485-"terminals on frequency inverter are the communication interfaces of Modbus
(2) Topological mode
It is a "Single-master Multi-slave" system. In this network, every communication machine has a
unique slave address. One of them is as "master" (usually PC host machine, PLC and HMI, etc.), actively
sends out the communication, to read or write the parameters of slave. Other machines will be used as
slave and response to the inquiry/command from master. At one time only one machine can send the data
and other machines are in the receiving status. The setup range of slave address is 0 to 247. Zero refers to
broadcast communication address. The address of slave must is exclusive in the network.
(3) Transmission mode
There provide asynchronous series and half-duplex transmission mode. In the series asynchronous
communication, the data is sent out frame by frame in the form of message. According to the Modbus-RTU
protocol, when the free time of no transmission in communication data lines is more than the transmission
time of 3.5byte, it indicates that a new start of communication frame.
The series inverter has built-in the Modbus-RTU communication protocol, and is applicable to
response the slave "Inquiry/command" or doing the action according to the master's "Inquiry / Command"
and response to the data.

Chapter 9 Appendix

Chapter 9 Appendix
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