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B1. Fundamental Principles
MODBUS Communications Protocol
B
VFD provides RS485 communication interface and supports Modbus communication protocol. Through the
protocol interface , the user can use the upper computer to send the operation command of VFD, read or modify
the function code parameters and view the working state and fault information of the VFD, and realize the
industrial field centralized control.
Topology : In the single host multi-slaves system, the slave address is unique, and the slave address range is from
1 to 247,0 as the broadcast address. A host refers to a personal computer or a programmable logic controller (PLC),
etc. slave refers to the VFD. The host can not only communicate with one slave, but also publish the broadcast
information to all slaves.
Interface mode: RS485 hardware interface.
Transmission mode: Asynchronous serial half-duplex transmission mode, at a time the host and slave can only be
sent by one data, another to receive data.
Data and frame format: VFD adopts RTU mode, data bit - 8; odd-even check -no parity check; stop bit – 1; the
baud rate is 1200, 2400, 4800, 9600, 19200, 38400, 57600 bps optional. RTU data frame, using CRC check,
every frame begins with of a pause interval of at least 3.5 characters, and after the last transmission of CRC
data, a pause of at least 3.5 characters represents the end of the message. The information of a frame must
be transmitted in the form of a continuous data stream. If there is a time interval of more than 1.5 characters
before the end of the transmission of the whole frame, the receiving device considers that the message frame is
incomplete. The message frame is discarded.
