Goodrive300-LIFT series inverter
Communication protocol
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10.3
Application of the inverter
The Modbus protocol of the inverter is RTU mode and the physical layer is RS485.
10.3.1 RS485
The interface of RS485 works on semiduplex and its data signal applies differential transmission
which is called balance transmission, too. It uses twisted pairs, one of which is defined as A (+) and
the other is defined as B (-). Generally, if the positive electrical level between sending drive A and B is
among +2
–
+6V, it is logic "1", if the electrical level is among -2V
–
-6V, it is logic "0".
485+ on the terminal board corresponds to A and 485- to B.
Communication baud rate means the binary bit number in one second. The unit is bit/s (bps). The
higher the baud rate is, the quicker the transmission speed is and the weaker the anti-interference is.
If the twisted pairs of 0.56mm (24AWG) is applied as the communication cables, the Max.
Transmission distance is as below:
Baud rate
Max. transmission
distance
Baud rate
Max. transmission
distance
2400BPS
1800m
9600BPS
800m
4800BPS
1200m
19200BPS
600m
It is recommended to use shield cables and make the shield layer as the grounding wires during
RS485 remote communication.
In the cases with less devices and shorter distance, it is recommended to use 120
Ω
terminal resistor
as the performance will be weakened if the distance increase even though the network can perform
well without load resistor.
10.3.2.1 Single application
Figure 10-1 is the site Modbus connection figure of single inverter and PC. Generally, the computer
does not have RS485 interface, the RS232 or USB interface of the computer should be converted into
RS485 by converter. Connect the A terminal of RS485 to the 485+ terminal of the inverter and B to the
485- terminal. It is recommended to use the shield twisted pairs. When applying RS232-RS485
converter, if the RS232 interface of the computer is connected to the RS232 interface of the converter,
the wire length should be as short as possible within the length of 15m. It is recommended to connect
the RS232-RS485 converter to the computer directly. If using USB-RS485 converter, the wire should
be as short as possible, too.
Select a right interface to the upper monitor of the computer (select the interface of RS232-RS485
converter, such as COM1) after the wiring and set the basic parameters such as communication baud
rate and digital check bit to the same as the inverter.
