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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) Interface mode
RS485 hardware interface
(2) 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
(3) 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.
I-1-2 Communications connection
(1)Interface mode: RS485 hardware interface
(2) Transmission mode:
Asynchronous serial, half duplex transmission mode. At the same time the host and slave can
only have one send data and the other can only receive data. Data in the process of serial
asynchronous communication, is in the form of a message, a frame of a frame to send.
(3)Topological structure:
Single host machine system. The set range from the machine address is 1~247, 0 for the
broadcast communication address. The slave address in the network must be unique.
Single application
Picture I-3 , the MODBUS wiring diagram of single inverter and PC. Generally , because PC
does not carry RS485 interface, So we need to change the RS232 interface or USB interface in PC
to RS485 through coverter . Connect the A terminal of RS485 to 485+ terminal on terminal
board ,and connect the B terminal of RS485 to 485- terminal on terminal board. It is better to use
twisted-pair cable with shield for the connection. When using the RS232-485 converter, the cable
between RS232 interface on PC and RS232 interface on RS232-RS485 converter should be short,
not longer than 15m.The best way is to insert the RS232-RS485 converter on the PC. When using
the USB-RS485 converter, the cable should be short too.
When all cable is in right position, choose the right terminal on PC, the terminal forconnecting
RS232-RS485 converter, such as COM1, and set the basic parameters such as baud rate and data
