Read/Write Memory - Four Register Write Command (31)

When large values are processed using different data formats (e.g., float32 vs. int64), minor differences may occur due to internal calculation methods, typically less than 1/10,000, and are considered normal.

This command applies only to memory items with a register length of 4. Refer to the parameter list for details.

Function Code 31

The Four Register Write command (Function Code 31) writes 4 consecutive registers (64-bit), supporting Int64 or other 64-bit values. It is recommended for writing large parameters such as: D11 Total Target (64-bit), C04 Dosing Target (64-bit)

A standard 32-bit floating-point number (Function Code 30) has a precision of about 7 significant digits. When the value exceeds ten million, using 32-bit floats may cause accuracy loss and rounding errors.

In such cases, it is recommended to use Function Code 31 with 64-bit integers (Int64) to ensure the data is accurately stored in memory without any rounding errors.

Function Code 31 uses a mirror-response mechanism. When the write is successful, the RX response frame from the slave will exactly match the TX request in both format and content.

Read/Write Memory – Four Register Write Command (Function Code 31) Format

This example demonstrates how the master uses Function Code 31 to write a target value of +999,999,999 to the parameter C04 Dosing Target.

• Register Address: 02 83

• Register Length: 4 (4 consecutive registers, 64-bit)

• Data Type: Int64

1. Value Conversion and Data Preparation (Hex Data)

• Target Value: 999,999,999 (decimal)

• Hex Conversion: 3B 9A C9 FF。

• Packed in Int64 Format (8 Bytes): Since Function Code 31 requires 8 bytes, prepend zeros: Complete 64-bit Data: 00 00 00 00 3B 9A C9 FF

2. Master Sends Write Command (TX Frame)

TX： 01 31 02 83 00 00 00 00 3B 9A C9 FF 0B 7A

• Slave Address: 01 (Flow meter address)

• Function Code: 31 (Write 4 Registers)

• Starting Register Address: 02 83 (C04 Dosing Target 64-bit memory address)

• Data to Write: 00 00 00 00 3B 9A C9 FF (C04 Dosing Target 64-bit value)

• CRC: 0B 7A (Calculated CRC for error checking)

3. Slave Response (RX Frame)

When the write is successful, the slave echoes the TX frame for verification.

RX: 01 31 02 83 00 00 00 00 3B 9A C9 FF 0B 7A