AL4042
Remote I/O module 16 DI
40
9.3.2 Device-specific notes
9.3.2.1 Rules for accessing the Modbus register
The following rules apply for access to the Modbus registers:
u
To read or write Modbus registers, use only the valid Function Codes
.
9.3.2.2 Supported function codes
The device supports the following function codes for accessing the Modbus registers:
Function code
Name
Description
FC2 (0x02)
Read Input Discretes
Read individual digital inputs
FC3 (0x03)
Read Multiple Registers
Read several contiguous registers
FC4 (0x04)
Read input register
Read input register
FC6 (0x06)
Write Single Register
Writing a single register
FC16 (0x10)
Write Multiple Registers
Writing several contiguous registers
FC23 (0x17)
Read / Write Multiple Registers
Read / write several contiguous registers
FC43 (0x2B)
Read Device Identification
Reading device information
Detailed information about the function codes:
Ò
Modbus TCP- specification
9.3.2.3 Exception codes
A Modbus TCP request has the following structure:
Function
Code
Request Data
A Modbus TCP response has the following structure:
Function
Code
Response Data
When a request is processed without errors, the response message contains the following information:
•
Function code (1 byte): Function code of the request message
•
Response data (n bytes): Requested data
If an error occurs during the processing of a request, the response message contains the following
information:
•
Function code (1 byte): Error Code (= Request Function Code + 0x80)
•
Response data (1 byte): Exception codes
