Data Addresses In Modbus Messages; Supported Function Codes - ABB RS485 Installation And Startup Manual

5.2 Data Addresses in Modbus Messages

Modbus defines 4 address spaces: 2 address spaces for bit addressable data and 2
address spaces for 16 bits addressable data.
Address space
0XXXX
1XXXX
3XXXX
4XXXX

5.3 Supported function codes

The following table gives the Modbus functions, which are implemented and supported.
The code is the one used in function field of the Modbus message.
The address space concerned and the purpose of the function are given below.
Code Function
1 Read Coil Status
2 Read Input Status
3 Read Holding Registers
4 Read Input Registers
5 Force Single Coil
6 Preset Single Register
7 Read Exception Status
8 Diagnostics
11 Fetch Comm. Event Ctr.
12 Fetch Comm. Event Log
15 Force Multiple Coils
16 Preset Multiple Registers
17 Report Slave ID
22 Mask Write 4X registers
23 Read/Write 4X registers
Data Readable/writable
Output bit Read & write
Input bit Read
Input word Read
Output word Read & write
Address range/remark
0XXXX Reads the on/off status of discrete outputs
1XXXX Reads the on/off status of discrete inputs
4XXXX Reads contents of output registers
3XXXX Reads contents of input registers
0XXXX Sets the status of a discrete output
4XXXX Sets the value of a holding register
Device specific (see Modbus data table of a device)
Checks the communication system between the master and the slave
Returns amount of successful read/write operations on data points
Returns log registers of communication events
0XXXX Sets the status of multiple discrete outputs
4XXXX Sets the value of multiple holding registers
Device specific (see Modbus data table of the device)
4XXXX And/Or write of a holding register
4XXXX Reads a set of holding registers and writes a set of holding
registers in one query
Modbus name
Coil Status
Input Status
Input Register
Holding Register
RS485  Modbus protocol overview - 15