GD310-UL series VFD
Communication protocol
-190-
10.3 Application of the VFD
The Modbus protocol of the VFD 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) are 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 1 is the site Modbus connection figure of single VFD 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 VFD 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 VFD.
Summary of Contents for GD310-011P-4-UL
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