Modbus Function Code 16

Write Multiple Holding Registers on Modbus

This function code is used to write a block of contiguous registers (1 to 123 registers) in a remote device. The requested written values are specified in the request data field. Data is packed as two bytes per register.

Request

Function code	1 Byte	0x10
Starting Address	2 Bytes	0x0000 to 0xFFFF
Quantity of Registers	2 Bytes	0x0001 to 0x007B
Byte Count	1 Byte	2 x N*
Registers Value	N* x 2 Bytes	value

*N = Quantity of Registers
Table 1 - Command structure

Response

The normal response returns the function code, starting address, and quantity of registers written.

Function code	1 Byte	0x10
Starting Address	2 Bytes	0x0000 to 0xFFFF
Quantity of Registers	2 Bytes	1 to 123 (0x7B)

Table 2 - Response structure

Error

Error code	1 Byte	0x90
Exception code	1 Byte	01 or 02 or 03 or 04

Table 3 - Error structure. Scroll below for details.

Example

Request

This command is writing the contents of two analog output holding registers # 40019 & 40020 to the slave device with address 11. Each holding register can store 16 bits.

0B 10 0012 0002 04 0B0A C102 A0D5

• 0B: The Slave Address (0B hex = address 11)
• 10: The Function Code 16 (Write Multiple Holding Registers, 16 = 10 hex)
• 0012: The Data Address of the first register (0012 hex = 18, +40001 offset = register #40019).
• 0002: The number of registers to write.
• 04: The number of data bytes to follow (2 registers x 2 bytes each = 4 bytes).
• 0B0A: The value to write to register 40019
• C102: The value to write to register 40020
• A0D5: The CRC (Cyclic Redundancy Check) for error checking.

Response

0B 10 0012 0002 E167

• 0B: The Slave Address (0B hex = address 11)
• 10: The Function Code 16 (Write Multiple Holding Registers, 10 hex - 16)
• 0012: The Data Address of the first register (# 40019 - 40001 = 18 (0012 hex) ).
• 0002: The number of registers written.
• E167: The CRC (Cyclic Redundancy Check) for error checking.

Workflow Diagram for Modbus FC 16

Contents retrieved from

• http://modbus.org/
• http://www.simplymodbus.ca/

More information

• Modbus Function Codes
• Mobdbus function code 1 - read coils
• Mobdbus function code 2 - read discrete inputs
• Mobdbus function code 3 - read multiple holding registers
• Mobdbus function code 4 - read input registers
• Mobdbus function code 5 - write single coil
• Mobdbus function code 6 - write single holding register
• Mobdbus function code 15 - write multiple coils
• Mobdbus function code 16 - write multiple holding registers
• Modbus References
• Modbus protocol basics