INVT Goodrive3000 Series, Руководство по эксплуатации

Страница: 200 / 251

Goodrive3000 series medium voltage VFD Moudbus protocol
-194-
INVT
VFD
Address 1
Ground
485 +
485-
Ground
485+
485 -
Ground
485 +
485-
120
Ω
Terminal
resistor
PC
Converter
GND
RS232- 485
RS cable max.
length
:
15m
Shielded twisted pair
Address 2 Address n
INVT
VFD
INVT
VFD
Figure 8-4 Practical application diagram of chrysanthemum link connection
Figure 8-1 shows the start connection diagram. When this connection mode is adopted, each of the two devices that are
farthest away from each other on the line must be configured with a terminal resistor (in this figure, the two devices are
devices 1# and 15#).
1#
15#
32#
6
#
M
ain co
ntr
ol
de
vic
e
Figure 8-1 Star connection
Use shielded cable, if possible, in multi-device connection. The baud rates, data bit check settings, and other basic
parameters of all the devices on the RS485 line must be set consistently, and addresses cannot be repeated.
8.3.2 RTU mode
8.3.2.1 RTU communication frame structure
When a controller is set to use the RTU communication mode on a Modbus network, every byte (8 bits) in the message
includes 2 hexadecimal characters (each includes 4 bits). Compared with the ASCII mode, the RTU mode can send more
data at the same baud rate.
Code system
• 1 start bit
• 7 or 8 data bits; the minimum valid bit is transmitted first. Each frame domain of 8 bits includes 2 hexadecimal characters
(0
–9, A–F).
• 1 odd/even check bit; this bit is not provided if no check is needed.
• 1 end bit (with check performed), 2 bits (without check)
Error detection domain
• Cyclic redundancy check (CRC)
The following table describes the data format.
11-bit character frame (Bits 1 to 8 are data bits)
Start bit BIT1 BIT2 BIT3 BIT4 BIT5 BIT6 BIT7 BIT8 Check bit Stop bit
10-bit character frame (Bits 1 to 7 are data bits)
Start bit BIT1 BIT2 BIT3 BIT4 BIT5 BIT6 BIT7 Check bit Stop bit
In a character frame, only the data bits carry information. The start bit, check bit, and end bit are used to facilitate the
transmission of the data bits to the destination device. In practical applications, you must set the data bits, parity check
bits, and stop bits consistently.
In RTU mode, a new frame always must be preceded by a time gap with a minimum length of 3.5 bytes. On a network