ICPDAS ET-2268 CR User Manual page 137

ET-2200 Series Ethernet I/O Modules
 Modbus RTU Data Structure
Byte 06
Net ID
(Station Number)

Net ID: Specifies the address of the receiver (i.e., the Modbus/TCP slave).

Function Code: Specifies the message type.

Data Field: The data block.
Net ID (Station Number)
The first byte in the frame structure of a Modbus RTU query is the address of the receiver. A valid
address is in the range of 0 to 247. Address 0 is used for general broadcast purposes, while addresses
1 to 247 are assigned to individual Modbus devices.
Function Code
The second byte in the message structure of a Modbus RTU query is the function code, which
describes what the slave device is required to do. Valid function codes range between 1 and 255. To
answer the query, the slave device uses the same function code as contained in the request. The
highest bit of the function code will only be set to '1' if an error occurs in the system. In this way, the
master device will know whether or not the message has been correctly transmitted.
Code
01 (0x01) Read the Status of the Coils (Read DO Readback values)
02 (0x02) Read the Status of the Input (Read DI values)
03 (0x03) Read the Holding Registers (Read AO Readback values)
04 (0x04) Read the Input Registers (Read AI values)
05 (0x05) Force a Single Coil (Write DO value)
06 (0x06) Set a Single Register (Write AO value)
15 (0x0F) Force Multiple Coils (Write DO values)
16 (0x10) Set Multiple Registers (Write AO values)
Copyright © 2023 ICP DAS CO., Ltd. All Rights Reserved.
Byte 07
Function Code
Reference Number
(Address Mapping)
Function
Bytes 08 - 09
Data Field
Bytes 10 - 11
Number of Points
Reference
(Address)
0xxxx
1xxxx
4xxxx
3xxxx
0xxxx
4xxxx
0xxxx
4xxxx
-137 -