Appendix A Modbus Communication Protocol - Veikong VFD500 Series User Manual

VFD500 high performance vector control frequency inverter user manual Appendix A Modbus communication protocol

Appendix A Modbus communication protocol

VFD500 series of inverter provides RS485 communication on 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. In addition
VFD 500can also be used as a host to broadcast with other VFD500 communication.
A.1
Protocol format
RS485 asynchronous half-duplex.
RS485 terminal default data format: 1-8-N-1 (1 start bit, 8 data bits, no parity, 1 stop bit), the default
baud rate: 9600bps. See parameter group set 30.
A.2
Message format
The VFD500 series inverter Modbus message includes the start sign, the RTU message, and the
end sign。
The RTU message includes the address code, the PDU (Protocol Data Uint, the protocol data unit),
and the CRC check. PDU includes the function code and the data section.
RTU frame format：
Frame start (START)
Target station address
(ADR)
Command code
(CMD)
Number of function
code
CRC CHK low level
CRC CHK high level
FRAME END
A.3 Command code instruction
More than the 3.5 byte transmission time
Communication address:1 to 247(0: broadcast address)
Command
code
0x03 Read multiple registers of the AC drive
0x06 Write a single register to the AC drive.
0x10 Write Multiple registers to the AC drive.
0x08 Diagnostic command code
Including the register address (2Byte), the number of registers n(2Byte)
and the register content (2nByte), etc. see A3 in detail
It indicates the replying data or the data waiting to
write-in. CRC 16 check value, During the transmission, high bit is put in
front and low bit is at the back. see detail in A.5 Chapter
More than 3.5 byte transmission time
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Description