When RS485 interfaces are used for long-distance communication, it is recommended that you use
shielded cables, and use the shield layer as the ground wires.
When there are fewer devices and the transmission distance is short, the whole network works well
without terminal load resistors. The performance, however, degrades as the distance increases.
Therefore, it is recommended that you use a 120 Ω terminal resistor when the transmission distance
is long.
9.3.1.1 Application to one VFD
Figure 9-2 is the Modbus wiring diagram of one VFD and a PC. Generally, PCs do not provide RS485
interfaces, so you need to convert an RS232 interface or USB port of a PC to an RS485 interface.
Connect end A of the RS485 interface to the 485+ port on the terminal block of the VFD, and connect
end B to the 485- port. It is recommended that you use shielded twisted pairs. When an RS232-RS485
converter is used, the cable used to connect the RS232 interface of the PC and the converter cannot
be longer than 15 m. Use a short cable when possible. It is recommended that you insert the converter
directly into the PC. Similarly, when a USB-RS485 converter is used, use a short cable when possible.
Figure 9-1 Wiring of RS485 applied to one standard model VFD
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