Modbus Features; Data Objects; Function Codes; Data Field - Danfoss iC7 Series Operating Manual

iC7 Series Modbus
Operating Guide

7 Modbus Features

7.1 Data Objects

Table 28: Supported Modbus Object Types
Object type
Coil
Input register
Holding register

7.2 Function Codes

The function code of a message frame contains 8 bits. Valid codes are in the range of 1–FF. Use function codes to send messages
between client and server. When a message is sent from a client to a server device, the function code tells the server which action to
perform. When the server responds to the client, it uses the function code to indicate either a normal (error-free) response, or that
some error occurred (called an exception response). For a normal response, the server echoes the original function code. For an
exception response, the server returns a code that is equivalent to the original function code with its most significant bit set to logic
1. Furthermore, the server places a unique code into the data field of the response message. It tells the client which error occurred,
or the reason for the exception.
Header
7 bytes
Illustration 15: Modbus TCP Frame
Table 29: Supported Modbus Function Codes
Function code Modbus object type
Dec Hex
1 1 Read coils
3 3 Read multiple holding registers
4 4 Read input registers
5 5 Write single coils
6 6 Write single holding register
15 F Write multiple coils
16 10 Write multiple holding registers
23 17 Read/write multiple registers
43 2B Read device ident

7.3 Data Field

The data field is constructed using sets of 2 hexadecimal digits in the range of 00–FF hexadecimal. These digits are made up of 1
TCP character. The data field of messages sent from a client to a server device contains extra information, which the server must use
to act as defined by the function code. It can include items such as coil, or register addresses, the quantity of items to be handled,
and the count of actual data bytes in the field.
40 | Danfoss A/S © 2023.09
Access
Read/write
Read only
Read/write
Function Code
1 byte
Data
n bytes
Access type
Discrete (1 bit)
Register (16 bit)
Register (16 bit)
Discrete (1 bit)
Register (16 bit)
Discrete (1 bit)
Register (16 bit)
Register (16 bit)
MEI
AQ456329149698en-000101 / 136R0334
Modbus Features
Size
1 bit
16 bits
16 bits
Address range
00001–09999
40001–49999
30001–39999
00001–09999
40001–49999
00001–09999
40001–49999
40001–49999
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