Modbus Smart Water Meter Communication Protocol Four Wires

Modbus water meter communication protocol

Introduction of RS485 module

Four wires: RS485 needs four wires, of which the second wire is rs485a, rs485b, the second wire is positive and negative 12V power line, the pulse signal line is not divided into positive and negative poles, and the 485 communication line is connected. Red (12V positive), blue (12V negative), yellow (485a), green (485b). Note: wiring must be done carefully! An error will result in damage to the instrument module.

The module integrates the pulse counting module, and outputs the accumulated pulse in RS485 or MBus mode, generally using RS485 Modbus communication protocol or 188 protocol.

When the communication line is long, the cross-sectional area of the communication wire should be increased, the communication line should avoid high-power electrical equipment and strong interference sources, and do a good job in waterproof protection.

Communication settings

1. Baud rate: 9600 / 4800 / 1200 (default 9600 cannot be changed)

2. Check: no check (default no check)

3. Data bit: 8

4. Stop bit: 1

Modbus Protocol

1. Read operation (03h)

	Function code	First register high bit address	First register low address	The high order of the number of registers	The low order of the number of registers	CRC check low bit	CRC check high bit

2. Read operation reply(03H)

	Function code	Number of bytes	Data high byte		Data low byte	CRC check low bit	CRC check high bit

3. Write operation (06h)

	Function code	First register high bit address	First register low address	Data high byte	Data low byte	CRC check low bit	CRC check high bit

4. Write operation reply(06H)

	Function code	First register high bit address	First register low address	Data high byte	Data low byte	CRC check low bit	CRC check high bit

5. Write operation (10h)

	Function code	First register high bit address	First register low address	The high order of the number of registers	The low order of the number of registers	Number of bytes	Data high byte		Data low byte	CRC check low bit	CRC check high bit

6. Write operation reply (10h)

	Function code	First register high bit address	First register low address	The high order of the number of registers	The low order of the number of registers	CRC check low bit	CRC check high bit

7. Exception code

	Function code	Exception code	CRC check low bit	CRC check high bit
		01h illegal function 02h illegal data address 03h illegal data value

8. Register address

	Register address	Number of bytes
Device address			Read / write	Not recommended
Cumulative flow			Read / write

Be careful:

The exception code is the highest bit plus 1 of the normal function code. For example, the exception code of the read operation 03h is 83h, the exception code of the write single word 06h is 86h, and the exception code of the write multiple word 10h is 90h.

The cumulative flow is a 4-byte hexadecimal number, with the high bit first and the low bit last. The cumulative flow uses 32-bit data (2 words) without sign.

For example, if the actual data is 123456, the high bit word is saved as 0x0001, and the low bit word is saved as 0xe240.

Unit of measurement: according to the ratio you write, this meter does not participate in the calculation, only records the actual pulse value.

For example:

Suppose the table address is 01 (table address range 1-247)

1. Write the base number of water meter 123456 (hexadecimal: 01e240h)

01 10 02 00 02 00 01 E2 40 73 86 13 bytes

Write the base number of water meter to return: 01 10 02 00 02 E1 B0 8 bytes

Exception: 01 90 03 0C 01 5 bytes (illegal data value)

2. Water meter reading: 01 03 02 00 02 64 73 8 bytes

Read Cumulative Return: 01 03 04 00 01 E2 40 E2 A3 9 bytes

Exception: 01 83 03 01 31 5 bytes

3. Reading water meter address: 00 03 02 00 01 84 63 8 bytes

Return: 01 03 02 00 01 79 84 7 bytes

be careful! When reading the water meter address, only one water meter can be connected to the bus.

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