Modbus Tcp/ Udp Mbap Header; Supported Modbus Function Codes - Hitachi HX-RIO3 Series User Manual

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6.1.2. MODBUS TCP/ UDP MBAP Header

The MBAP (MODBUS Application Protocol) header contains the following fields.
Fields Length
Transaction
2bytes
Identifier
Protocol
2bytes
Identifier
Length 2bytes
Unit
1byte
Identifier
• Transaction Identifier - It is used for transaction pairing; the MODBUS server copies in the response the
transaction identifier of the request.
• Protocol Identifier – It is used for intra-system multiplexing. The MODBUS protocol is identified by the value
0.
• Length - The length field is a byte count of the following fields, including the Unit Identifier and data fields.
• Unit Identifier – This field is used for intra-system routing purpose. Typically, MODBUS server must be
returned with the same value set by MODBUS client.

6.2 Supported MODBUS Function Codes

Function
Function
Code
1(0x01) Read Coils
2(0x02) Read Discrete Inputs
3(0x03) Read Holding Registers
4(0x04) Read Input Registers
5(0x05) Write Single Coil
6(0x06) Write Single Register
8(0x08) Diagnostics
15(0x0F) Write Multiple Coils
16(0x10) Write Multiple registers
23(0x17) Read/Write Multiple registers
- Refer to MODBUS APPLICATION PROTOCOL SPECIFICATION V1.1a
Description
Identification of a MODBUS
Request /Response
transaction.
0 = MODBUS protocol
Number of following bytes
Identification of a remote
slave connected on a serial
line or on other buses.
Client
Initialized by
the client
Initialized by
the client
Initialized by
the client
(Request)
Initialized by
the client
Description
Read output bit
Read input bit
Read output word
Read input word
Write one-bit output
Write one-word output
Read diagnostic register
Write a number of output bits
Write a number of output words
Read a number of input words /Write a number of output
words
HX-RIO3 Series
Server
Recopied by the server from the
received
Recopied by the server from the
received
Initialized by the server
(Response)
Recopied by the server from the
received