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Appendix I RS485 Communication protocol
I-1 Communication protocol
I-1-1 Communication content
This serial communication protocol defines the transmission information and use format in the series communication
Including: Master polling( or broadcast) format; master encoding method, and contents including: function code of action,
transferring data and error checking. The response of slave also adopts the same structure, and contents including:
Action confirmation, returning the data and error checking etc. If slave takes place the error while it is receiving information
or cannot finish the action demanded by master, it will send one fault signal to master as a response.
Application Method
The inverter will be connected into a “Single-master Multi-slave” PC/PLC control network with RS485 bus.
Bus structure
(1) Transmission mode
Asynchronous series and half-duplex transmission mode. For master and slave, only one of them can send the
data and the other only receives the data at the same time. In the series asynchronous communication,
the data is sent out frame by frame in the form of message
(2) Topological structure
Single-master and multi-slave system. The setting range of slave address is 0 to 247, and 0 refers to broadcast
communication address. The address of slave for network must be exclusive.
Figure I-3 is the single inverter and PC set up MODBUS field wiring diagram. Because computers are generally not with
RS485 interface, the computer must be built-in RS232 interface or USB interface through the converter to convert to
RS485. Connect the T + of converter with 485 + terminal of the inverter, Connect the T- of converter with 485- terminal
of inverter. We recommended to use a shielded twisted pair. When adopting the RS232-485 converter,RS232 interface
connected with RS232-RS485 RS232 interface, the cable should be as short as possible,15meters at the longest, we
recommend to plug the RS232-RS485 with computer in pair directly. Similarly, when using the USB-RS485 converter,
cable should be as short as possible.
When the line is connected, connect the right port of the host computer on the computer to (RS232-RS485 converter
port, such as COM1), and set the basic parameters and the baud rate and data bit parity and so on consistent with the
inverter.
RS232 to RS485 converter
T +
T -
485 485+
RS232 cable 15m
at the longest
Shielded twisted pair
Frequency inverter
PE
-
Figure I-3
