Appendix Ii Rs485 Communication Protocol; Ii -1 Communication Protocol - Powtran PI500-S Series Manual

Appendix II RS485 Communication protocol

II -1 Communication protocol

II -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.
II-1-2 Communication connection
Standalone method
Figure II- 1 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 cable 15m
at the longest
RS232 to RS485 converter
T+
T-
Figure II- 1
71
Shielded twisted pair
PE
SG- SG+
Frequency
inverter