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# Read/Write Memory - Write Multiple Registers Command (16)
{% hint style="info" %}
Function Code 16 (0x10) is the **standard** Modbus "Write Multiple Registers" command, supported by virtually every PLC and HMI. Since Function Codes 30 and 31 are proprietary short-frame formats that many PLCs cannot generate, Function Code 16 provides a standards-compliant alternative path to write the exact same parameters at the exact same addresses — only the frame format differs.
{% endhint %}
#### Function Code 16
The Write Multiple Registers command (Function Code 16) writes data to one or more consecutive registers using a standard, variable-length Modbus frame. Unlike Function Codes 06, 30, and 31 — each fixed to one specific data width — Function Code 16 can write Int16 (1 register), Float32 (2 registers), or Int64 (4 registers) values, matching whatever width the target parameter requires. \
Data type ranges match those described under Function Codes 06, 30, and 31. \
Examples: Set A15 Damping to 10, A18 Low Flow Cutoff to +5.5, or C04 Dosing Target to 999,999,999.
#### Read/Write Memory – Write Multiple Registers Command (16) Format
***
## Modbus RTU Read/Write Memory – Write Multiple Registers Command (Function Code 16)
### **Example 1 —** 16-bit: A15 Damping
This example shows the master using **Function Code 16** to write **10** to the parameter **“A15 Damping”**.
According to the Read/Write Memory List:
* **Starting Address:** 00 12
* **Register Length:** 1
* **Data Type:** Int16
#### 1. Value Conversion and Data Preparation (Hex Data)
Convert the decimal value **10** to **Int16 (Big Endian)** format.
$$
10 ₁₀ = 000A ₁₆
$$
The resulting 2-byte data is:： `00` `0A`。
#### 2. Master Sends Write Command (TX Frame)
The master uses Function Code 16 with a Byte Count of 02, writing 4 data bytes to two registers starting at address 00 15.
```
TX: 01 10 00 12 00 01 02 00 0A 25 25
```
* Slave Address: `01`
* Function Code: `16` (0x10)
* Starting Register Address: `00 12` (A15 Damping)
* Quantity of Registers: `00 01`
* Byte Count: `02`
* Written Data: `00 0A` (10 in decimal)
* CRC: `25 25` (calculated CRC)
#### 3. **Slave Response (RX Frame)**
When the write command is successful, the master receives a response from the slave as confirmation.
```
RX: 01 10 00 12 00 01 A1 CC
```
* Slave Address: `01`
* Function Code: `16` (0x10)
* Starting Register Address: `00 12` (A15 Damping)
* Quantity of Registers Written: `00 01`
* CRC: `A1 CC` (calculated CRC)
Once the master receives the RX frame and verifies that the **Starting Register Address**, and Quantity of Registers Written are correct, it confirms that **A15 Damping has been successfully set to 10**.
***
### **Example 2 —** 32-bit: A18 Low Flow Cutoff
This example shows the master using **Function Code 16** to write **+5.5** to the parameter **“A18 Low Flow Cutoff”**.
According to the Read/Write Memory List:
* **Starting Address:** 00 15
* **Register Length:** 2
* **Data Type:** : Float32
#### 1. Value Conversion and Data Preparation (Hex Data)
Convert the decimal value **+5.5** to **Float32** **(Big Endian)** format.
$$
5.5 ₁₀ = 40B00000 ₁₆
$$
The resulting 4-byte data is:： `40` `B0` `00` `00`。
#### 2. Master Sends Write Command (TX Frame)
The master uses Function Code 16 with a Byte Count of 04, writing 4 data bytes to two registers starting at address 00 15.
```
TX: 01 10 00 15 00 02 04 40 B0 00 00 26 BB
```
* Slave Address: `01`
* Function Code: `16` (0x10)
* Starting Register Address: `00 15` (A18 Low Flow Cutoff)
* Quantity of Registers: `00 02`
* Byte Count: `04`
* Written Data: `40 B0 00 00` (+5.5 in Float32)
* CRC: `26 BB` (calculated CRC)
#### 3. **Slave Response (RX Frame)**
When the write command is successful, the master receives a response from the slave as confirmation.
```
RX: 01 10 00 15 00 02 50 0C
```
* Slave Address: `01`
* Function Code: `16` (0x10)
* Starting Register Address: `00 15` (A18 Low Flow Cutoff)
* Quantity of Registers Written: `00 02`
* CRC: `50 0C` (calculated CRC)
Once the master receives the RX frame and verifies that the **Function Code**, **register address**, and **number of registers written** are correct, it confirms that **A18 Low Flow Cutoff has been successfully set to +5.5**.
---
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