TECHTOP TD20 Series Product Manual page 98

TD20 Series VFD Communication Protocol
distance is as below:
Baud Max.transmissio Baud Max.transmissio Baud Max.transmissio Baud Max.transmissio
rate n distance rate n distance rate n distance rate n distance
1920
2400 4800 9600
1800m 1200m 800m 0 600m
BPS BPS BPS
BPS
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 120Ω terminal resistor as
the performance will be weakened if the distance increase even though the network can perform well
without load resistor.
7.2.1.1 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.
Twisted pairs with shield screen
B
A
RS 485 Route
Earth
A
B
Earth
485- 485+
Converter from
RS232 to RS485
Computer
VFD
Figure 1 RS485 physical connection in single application
7.2.1.2 Multi-applications
In real multi-applications, the chrysanthemum connection and star connection are commonly used.
Chrysanthemum chain connection is required in the RS485 industrial fieldbus standards. The two ends
are connected to terminal resistors of 120Ω which is shown as figure 2.
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