Goodrive18 series two-in-one VFD Communication
-111-
Otherwise, one of the two communication channels fail.
7.2.1 Two-wire RS485
The two-wire RS485 interface works in half-duplex mode and sends data signals in the
differential transmission way, which is also referred to as balanced transmission. The two-wire
RS485 interface uses a twisted pair, in which one wire is defined as A (+), and the other B (-).
Generally, if the positive electrical level between the transmission drives A and B ranges from
+2V to +6V, the logic is "1"; and if it ranges from -2V to -6V, the logic is "0".
On the VFD terminal block, the 485+ terminal corresponds to A, and 485- corresponds to B.
The communication baud rate (P14.01) indicates the number of bits sent in a second, and the
unit is bit/s (bps). A higher baud rate indicates faster transmission and poorer anti-interference
capability. When a twisted pair of 0.56mm (24 AWG) is used, the maximum transmission
distance varies according to the baud rate, as described in the following table.
Max.
transmission
distance
Max.
transmission
distance
Max.
transmission
distance
Max.
transmission
distance
In long-distance RS485 communication, it is recommended that you use shielded cables, and
use the shielding layer as the ground wire. 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.
7.2.1.1 When one VFD is used
Figure 7.1 is the Modbus wiring diagram for the network with one VFD and PC. Generally, PCs
do not provide RS485 interfaces, and therefore you need to convert an RS232 or USB
interface of a PC to an RS485 interface through an adapter. Then, 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 adapter is
used, the cable used to connect the RS232 interface of the PC and the adapter cannot be
longer than 15m. Use a short cable when possible. It is recommended that you insert the
adapter directly into the PC. Similarly, when a USB-RS485 adapter is used, use a short cable
when possible.
When the wiring is completed, select the correct port (for example, COM1 to connect to the
RS232-RS485 adapter) for the upper computer of the PC, and keep the settings of basic
parameters such as communication baud rate and data check bit consistent with those of the
VFD.
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