TECHTOP TD20 Series Product Manual page 99

TD20 Series VFD
Twisted pair cables with shield screen
RS232-485
Converter
RSM15m
GND
Computer
Figure 3 is the star connection. Terminal resistor should be connected to the two devices which have
the longest distance. (1# and 15#device)
It is recommended to use shield cables in multiple connection. The basic parameter of the devices, such
as baud rate and digital check bit in RS485 should be the same and there should be no repeated
address.
7.2.2 RTU mode
7.2.2.1 RTU communication frame format
If the controller is set to communicate by RTU mode in Modbus network every 8bit byte in the message
includes two 4Bit hex characters. Compared with ACSII mode, this mode can send more data at the
same baud rate.
Code system
· 1 start bit
· 7 or 8 digital bit, the minimum valid bit can be sent firstly. Every 8 bit frame includes two hex
characters (0...9, A...F)
· 1 even/odd check bit . If there is no checkout, the even/odd check bit is inexistent.
· 1 end bit (with checkout), 2 Bit (no checkout)
Error detection field
· CRC
The data format is illustrated as below:
11-bit character frame (BIT1–BIT8 are the digital bits)
Start bit BIT1
485 +
485 -
Earth
VFD
Address 1
Figure 2 Chrysanthemum connection applications
1 #
32 #
Figure 3 star connection
BIT2 BIT3 BIT4
485 +
485 -
Earth
VFD
Address 2
Main control
device
15 #
BIT5 BIT6 BIT7
-97-
Communication Protocol
Ω
120
485 +
Terminal resistor
485 -
Earth
VFD
Address n
Check
BIT8 End bit
bit