Modbus TCP protocol | Schneider Electric LXM32M specification

LXM32M	3 Basics

3.2Modbus TCP protocol

The Modbus protocol defines a so-called Modbus PDU (Protocol Data Unit) which is independent of the underlying communication layers. This Modbus PDU consists of the fields "Function Code" and "Data". Depending on the mapping to the different network protocols, the Modbus PDU is extended by additional fields in the so-called Modbus ADU (Application Data Unit). The Modbus PDU and the Modbus ADU constitute the Modbus message, also referred to as "Frame".

	MODBUS TCP/IP ADU
MBAP Header	Function code	Data
		MODBUS PDU

Figure 3: Structure of a Modbus message

The "Function Code" of a message specified the Modbus service to be triggered. The "Data" field can contain additional information, depend- ing on the "Function Code".

Due to the encapsulation of "Function Code" and "Data" in the Mod- bus PDU, the Modbus services and the object model can be the same in the case of all Modbus versions.

In the case of a "Function Code" for which the "Data" field in the Mod- bus PDU has a fixed length, the "Function Code" is sufficient.

In the case of a "Function Code" for which the "Data" field in the Mod- bus request or the Modbus response has a variable amount of data, the "Data" field contains a byte counter.

The maximum size of a Modbus ADU is 260 bytes. The size of an embedded Modbus PDU is 253 bytes.

NOTE: The fields are encoded in Big Endian format (highest-value byte first).

0198441113843, V1.01, 01.2012

Modbus-TCP module

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Schneider Electric LXM32M manual Modbus TCP protocol, Structure of a Modbus message

Contents

LXM32M Important information Table of contents Diagnostics and troubleshooting Accessories and spare parts LXM32M About this manual Further reading Fieldbus products on the network Introduction LXM32M Intended use Before you begin safety informationQualification of personnel Hazard categories Basic information Standards and terminology Modbus TCP technology BasicsFunction principle Bus topology Client / server model Network service Snmp Structure of a Modbus message Modbus TCP protocol Field Length Description Mbap header Connection management Modbus TCP communication Excep Name Description Tion Code Modbus response to a Modbus request Address Value Reading and writing parameters 4 I/O scanning to Drive Profile Lexium Byte Meaning Data type Parameter address 4.1 I/O scanning Output Bit Meaning 4.2 I/O scanning Input Inputs Bit Signal Factory setting Parameter channel Ctrl Subindex Index Field Bytes Value Meaning Modbus services Function CodeFunction Code 3 Read Multiple Registers Sub-function Code Diagnostics function Function Code 8 Diagnostics Function Code 16 Write Multiple Registers Function Code 23 ReadWrite Multiple Registers Object ID Object name Value Function Code 43 Encapsulated Interface Transport Example of Function Code Examples LXM32M Description Order no InstallationInstallation of the module Pin Signal Meaning Electrical installation Commissioning the device Commissioning Switching on the device Power stage supply is switched off First Setup Manual assignment of the network address Bootp / boot BootpManual / MAnu Manual Dhcp / dhcP Dhcp IP address Ethernet module, byte Assignment of the network address via Bootp Assignment of the network address via Dhcp Setting the protocol Setting the transmission rate Set the IP address of the gateway with the parameters Setting the gateway Master with Word Swap Activating I/O scanning Setting I/O-ScanningSetting the master for I/O scanning Setting the mapping for I/O scanning PLC Setting communication monitoring for I/O scanning Setting the web server 0198441113843, V1.01 Operation Bit Name Meaning Operating statesIndication of the operating state Bit Name Meaning Operating state Changing the operating state Bit Name Description Indicating and monitoring the operating modeOperating modes Bit Name Description Starting and changing an operating mode MODE+ACTION Overview of operating modes Operating mode Jog Operating mode Electronic Gear 24 h Operating mode Profile Torque 23 h Operating mode Profile Velocity Operating mode Profile Position Operating mode Homing LXM32M6 Operation Operating mode Motion Sequence Web server Extended settings User interface Main menu Submenu Content FTP server Accessing the FTP server FDR service Fast Device Replacement LXM32M Fieldbus communication error diagnostics Diagnostics and troubleshooting Color Status Meaning Status LEDs Meaning for EtherNet/IP Meaning for Modbus TCP Color Error indication Excep Name Description Tion Code LXM32M Cables Accessories and spare parts LXM32M Units and conversion tables Glossary Rotation TemperatureTorque Moment of inertia Terms and Abbreviations LXM32M Index LXM32M