> For the complete documentation index, see [llms.txt](https://docs.lorric.com/qr/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.lorric.com/qr/fp-as310-paddle-wheel-flowmeter-manual-en-v1/communication/modbus-rtu-protocol.md).

# Modbus RTU Protocol

## Communications format

bit order: lsb first

byte order: big endian

Data bits:8 

Parity: None 

Stop bits: 1

Floating point number follows IEEE754-1985. The float32 below stands for 32bits Single precision floating point number.

## Terminology

‌‌Register: Length of 2 Byte or 16bit which is unit length of memory in Modbus RTU.

‌Byte: 8 bit length

## Definition and function of memory

#### **Modbus Memory Access**

Modbus-accessible memory is divided into **two main categories**: **read-only** and **read/write**.

* The **read-only memory** primarily contains data related to the **flow meter’s operational status**, such as **instantaneous flow rate**.\
  This category is the **most commonly accessed memory area**.\
  Read-only memory can **only be accessed using Function Code 04 (Read Input Registers)**.

Relevant register mappings and details can be found on the following page:


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