# Read-write memory read instruction(03)

{% hint style="info" %}
The length of total register requested by a single reading command must be less than or equal to 20 registers. Instructions longer than this will be ignored.
{% endhint %}

## **Instruction example** <a href="#instruction-example" id="instruction-example"></a>

**Format of command (03) from master**

| Byte#          | 1             | 2             | 3                                 | 4                                 | 5                                | 6                                | 7   | 8   |
| -------------- | ------------- | ------------- | --------------------------------- | --------------------------------- | -------------------------------- | -------------------------------- | --- | --- |
| Node ID        | Slave Address | Function Code | Address of first reading register | Address of first reading register | Quantity of registers to be read | Quantity of registers to be read | CRC | CRC |
| Example 01\~FF | 01            | 03            | 00                                | 00                                | 00                               | 03                               | 05  | CB  |

**Description of master command**

The example will read A01 pipe diameter options and A02 Scale Factor.

slave address: 01(address of this flowmeter)

function code: 03(read instruction)

Address of first reading register: 0000(Address of first register to read)

Quantity of registers to be read: 0003 (need to read 2 registers from 0000)

CRC: 05 CB (Calculating error correcting code according to CRC algorithm)

**Format of flowmeter response(03)**

| Byte#                       | 1             | 2             | 3                       | 4            | 5                         | 6                         | 7                         | 8            | 9                         | 10  | 11  |
| --------------------------- | ------------- | ------------- | ----------------------- | ------------ | ------------------------- | ------------------------- | ------------------------- | ------------ | ------------------------- | --- | --- |
| Node ID                     | Slave Address | Function Code | Amount of response Byte | Data Byte #1 | <p>Data Byte</p><p>#2</p> | <p>Data Byte</p><p>#3</p> | <p>Data Byte</p><p>#4</p> | Data Byte #5 | <p>Data Byte</p><p>#6</p> | CRC | CRC |
| <p>Example</p><p>01\~FF</p> | 01            | 03            | 06                      | 00           | 00                        | 3F                        | 80                        | 00           | 00                        | 2C  | 89  |

**Description of flowmeter response example**

slave address: 01(address of this flowmeter)

function code: 03(read instruction)

Amount of response Byte: 06 (3 register=6byte)

Data Byte:

* 00 00(Current pipe diameter is 1inch PVC)
* 3F 80 00 00(Current Scale Factor is 1.0)

CRC: 2C 89 (Calculating error correcting code according to CRC algorithm)


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