Instructions

14. Reference Guides
14.1. About Input Registers and Holding Registers
Modbus data is most oen read and wrien as registers which are 16-bit pieces of data.
Holding registers and Input registers are both 16-bit registers.
Input registers
Input registers can only be read.
Holding registers
Holding registers can be read or wrien.
These registers can be used for a variety of things such as inputs, outputs, conguraon data, or other
requirement for holding data.
14.2. Modbus Data Model
Discretes Input Single bit Read-Only Data can be provided by the I/O system.
Coils Single bit Read-Write Data can be alterable by the applicaon program.
Input Registers 16-bit word Read-Only Data can be provided by the I/O system
Holding Registers 16-bit word Read-Write Data can be alterable by the applicaon program.
Reference: MODBUS Applicaon Protocol Specicaon V1.1b3, April 26 2012
For more informaon refer to the Modbus organisaon website.
14.3. Modbus Transacons
Nr Transacon Funcon Code Descripon
1 Read Coils 0x01 Read from 1 to 2000 conguous status of coils in a remote device.
2 Read Discrete Inputs 0x02 Read from 1 to 2000 conguous status of discrete inputs in a remote device.
3 Read Holding Registers 0x03 Read the contents of a conguous block of holding registers in a remote device.
4 Read Input Registers 0x04 Read from 1 to 125 conguous input registers in a remote device.
5 Write Single Coil 0x05 Write a single output to ON or OFF in a remote device.
6 Write Single Register 0x06 Write a single holding register in a remote device.
15 Write Mulple Coils 0x0F In a sequence of coils, force each coil to either ON or OFF in a remote device.
16 Write Mulple
Registers
0x10 Write a block of conguous registers in a remote device.
22 Mask Write Register 0x16 In a single transacon, modify the contents of a specied holding register using a
combinaon of an AND mask, an OR mask, and the register's current contents.
Can be used to set or clear individual bits in the register.
23 Read/Write Mulple
Registers
0x17 Performs a combinaon of one read operaon and one write operaon.
The write operaon is performed before the read.
Reference: MODBUS Applicaon Protocol Specicaon V1.1b3, April 26 2012
For more informaon refer to the Modbus organisaon website.
Reference Guides Anybus
®
Communicator
™
- PROFIBUS to Modbus RTU/Serial
SCM-1202-177 1.2 Page 131 of 134