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5 Communication Protocol
5.1 RTU mode and format
When controller communicates via Modbus in RTU mode, each byte is divided into 2 hexadecimal
characters of 4 bits. The main advantage of this mode is that it can transfer characters with
higher density compared with ASCII mode given the condition of the same baud rate, and each
information must be transported continuously.
1) each byte format in RTU mode
Encoding system: 8 bits binary, hexadecimal 0-9, A-F.
Data bits: 1 bit of start bit, 8 bits of data (send from the lower bit), 1 bit of stop bit, optional
parity check bit (refer to bit sequence of RTU data frame).
Error check zone: cyclic redundancy check (CRC).
2) Bit sequence of RTU data frame
With parity check
Start 1 2 3 4 5 6 7 8 FAr Stop
Without parity check
Start 1 2 3 4 5 6 7 8 Stop
5.2 Register Address and Function Code
1) supported function code
Function code Function description
03 Read multiple registers
06 Write single register
10 Write multiple registers continuously
13 Read single parameter
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