Modbus RTU Protocol
Communication Format
Bit Order
lsb first
Data is transmitted starting from the Least Significant Bit (LSB).
Byte Order
big endian
Data is transmitted starting from the Most Significant Byte (MSB).
Data bits
8
Each character or byte consists of 8 data bits.
Parity
None
No parity bit is used for error checking during transmission.
Stop bits
1
1 stop bit is used at the end of each character.
Floating-Point Standard
IEEE 754-1985
Floating-point numbers (Float32) use the 32-bit single-precision format.
Register
2 Byte / 16 bit
Floating-point numbers (Float32) use the 32-bit single-precision format.
Byte
8 bit
The basic unit length of data transmission.
In Modbus RTU communication, a Register is the basic unit of memory communication, with a length of 2 bytes (16 bits). A Byte is the basic unit of data transmission, with a length of 8 bits.
Memory Definition and Functions
Modbus memory is divided into two categories, read-only and read-write.
Read-only type is mainly for flow meter status related memory, such as instantaneous flow rate. This is also the most commonly used memory. Refer to Read-only memory
Read-write memory is mainly to set-up parameters such as pipe diameter, and to reset variables, such as set zero on the cumulative flow. Refer to Read-Write Memory (RAM)
Read-write memory is only readable by using instruction 03. You can only change one parameter at a time with the write operation. If the length of the target register is 1, please use instruction 06. If the length is 2 registers, please use instruction 30. Refer to R
Memory Types
Read-Only Memory
Read/Write Memory
Main Functions
Read the device's real-time status and results.
Set the device's operating parameters and calibration values.
Stored Content
Stores memory related to flow status, such as instantaneous flow and totalized flow.
Stores memory related to flow configuration parameters, such as pipe diameter, calibration coefficients, and flow cutoff values.
Access Rights
Read-only: can only be read, not written
Read/Write: can be both read and written.
Function Codes
Read Command: 04 (Read Input Registers)
Read Command: 03 Write Command: 06 / 30 / 31
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