GN-9289 User Manual
Page 34 of (70)
G-series GN-9289 Modbus TCP_UDP Rev. 1.01.docx
8.2.
Supported MODBUS Function Codes
Function
Code
Function
Description
1(0x01)
Read Coils
Read output bit
2(0x02)
Read Discrete Inputs
Read input bit
3(0x03)
Read Holding Registers
Read output word
4(0x04)
Read Input Registers
Read input word
5(0x05)
Write Single Coil
Write one bit output
6(0x06)
Write Single Register
Write one word output
8(0x08)
Diagnostics
Read diagnostic register
15(0x0F)
Write Multiple Coils
Write a number of output bits
16(0x10)
Write Multiple registers
Write a number of output words
23(0x17)
Read/Write Multiple registers
Read a number of input words /Write a number of output words
- Refer to MODBUS APPLICATION PROTOCOL SPECIFICATION V1.1a
8.2.1.
1 (0x01) Read Coils
This function code is used to read from 1 to 2000 contiguous status of coils in a remote device. The Request
PDU specifies the starting address, i.e. the address of the first coil specified, and the number of coils. In the
PDU Coils are addressed starting at zero. Therefore coils numbered 1-16 are addressed as 0-15. The coils
in the response message are packed as one coil per bit of the data field. Status is indicated as 1= ON and
0= OFF.
Request
Field name
Example
Function Code
0x01
Starting Address Hi
0x10
Starting Address Lo
0x00
Quantity of Outputs Hi
0x00
Quantity of Outputs Lo
0x0A
Response
Field name
Example
Function Code
0x01
Byte Count
0x02
Output Status
0x55
Output Status
0x02
In case of address 0x1015~0x1000 output bit value: 10101010_01010101.
