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GD350A series high-performance multifunction VFD
-282-
1#
15#
32#
6
#
Main
control
device
Figure 9.5 Star connection
Use shielded cables, if possible, in multi-VFD 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
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 can help to send more data at the same baud rate.
Code system
•
1 start bit
•
7 or 8 data bits; the minimum valid bit is sent 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), or 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 stop bit are used