INVT Goodrive350 Series Operation Manual page 314

Goodrive350 IP55 High-ingress Protection Series VFD
Use shielded cables, 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.
9.3.2 RTU mode
9.3.2.1 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 achieves transmission of 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 stop 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
10-bit character frame (bits 1 to 7 are data bits):
Start bit Bit1
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.
Figure 9-5 Star connection
32#
Bit2 Bit3 Bit4
Bit2 Bit3 Bit4
1#
15#
Bit5 Bit6 Bit7
Bit5 Bit6
-296-
Communication protocol
Bit8 Check bit Stop bit
Bit7 Check bit Stop bit