HMS Networks Anybus Communicator ABC3028, User Manual

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Appendix A: Reference Guides 121 (124)
A Reference Guides
A.1 About Input Registers and Holding Registers
Modbus data is most often read and written 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 written.
These registers can be used for a variety of things such as inputs, outputs, configuration data, or
other requirement for holding data.
A.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 application 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 application program.
Reference: MODBUS Application Protocol Specification V1.1b3, April 26 2012
For more information refer to the Modbus organisation website.
A.3 Modbus Transactions
Nr
Transaction
Area
Function Code Description
1 Read Coils Coils 0x01 Read from 1 to 2000 contiguous status of coils in a
remote device.
2 Read Discrete
Inputs Discrete
inputs 0x02 Read from 1 to 2000 contiguous status of discrete
inputs in a remote device.
3 Read Holding
Registers Holding
registers 0x03 Read the contents of a contiguous block of holding
registers in a remote device.
4 Read Input
Registers Input registers 0x04 Read from 1 to 125 contiguous input registers in a
remote device.
5
Write Single Coil Coils 0x05 Write a single output to ON or OFF in a remote device.
6
Write Single
Register Holding
registers
0x06
Write a single holding register in a remote device.
15
Write Multiple
Coils Coils
0x0F
In a sequence of coils, force each coil to either ON or
OFF in a remote device.
16 Write Multiple
Registers Holding
registers 0x10 Write a block of contiguous registers in a remote
device.
23
Read/Write
Multiple Registers
Holding
registers 0x17 Performs a combination of one read operation and
one write operation.
The write operation is performed before the read.
43/14 Read Device
Identification N/A 0x2B/0x0E Read the vendor name, product code (article number),
firmware version, vendor URL and product name.
Reference: MODBUS Application Protocol Specification V1.1b3, April 26 2012
For more information refer to the Modbus organisation website.
Anybus
®
Communicator
™
User Manual
SCM-1202-162 1.1 en-US