Modbus Functions

FP Web-Server V2.11

 

 

12.1Overview on Modbus-TCP Functions of the FP Web-Server

General Information on Modbus-TCP

The Modbus-TCP is a standard global communication protocol (IAONA, Modbus-IDA) and is used to connect the PLC to third-party PLC equipment, SCADA systems, OPC servers, and Modbus-RTU gateways.

A Modbus-TCP server waits for an incoming connect from a Modbus-TCP client. Hence:

•A Modbus-TCP server (Ethernet) is comparable to a Modbus-RTU slave (serial).

•A Modbus-TCP client (Ethernet) is comparable to a Modbus-RTU master (serial).

A Modbus-TCP server is addressed with a unique IP address and a port number (default 502). Using a unit ID address in the Modbus-TCP data packet, various interfaces of the Modbus-TCP server can be addressed. The unit ID is comparable to the slave address in Modbus-RTU communication.

Modbus communication is based on a number of specified function codes which can address different data types. Which function codes and data types are supported depends on the unit implementation.

FP Web-Server Specific Implementation

The FP WEB Configurator Tool Version 2.1 allows you to configure the FP Web-Server (as an interface to the PLC) with the following Modbus-TCP server and client functions.

 

Function

 

 

Comment

 

A

A1

Modbus-TCP Server

 

Modbus-TCP Client → FP Web-Server → PLC (see

 

Modbus-TCP Server

 

 

 

note 2)

 

A2

Modbus-TCP Server

 

Modbus-TCP Client → FP Web-Server → multiple

 

(see page 146)

 

 

 

PLCs (see note 1 and note 2)

 

 

A3

Modbus-TCP Server

 

Modbus-TCP Client → FP Web-Server →

 

 

Gateway

 

Modbus-RTU Slave (see note 1)

 

B

B1

Modbus-TCP Client

 

PLC → FP Web-Server → Modbus-TCP Server

 

Modbus-TCP Client

B3

Modbus-TCP Client

 

Modbus-RTU Master (see note 1) → FP

 

Gateway

 

Web-Server → Modbus-TCP Server

 

(see page 148)

 

 

 

 

 

In addition: Modbus-RTU

B2

Modbus-RTU Master

 

PLC → FP Web-Server → Modbus-RTU Slave (see

 

functions (for PLCs that do

 

 

 

note 1)

 

not support Modbus-RTU

 

 

 

 

 

B4

Modbus-RTU Slave

 

Modbus-RTU Master (see note 1) → FP

 

protocol)

 

 

 

 

 

Web-Server → PLC

 

 

 

 

 

 

 

 

 

 

 

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