Search on WeChatTechnical Training1. Task Control Requirements Description

Use FX5U to achieve Modbus RTU communication with Mitsubishi E700 inverter, with functions: change frequency, forward, reverse, stop. As shown in Figure 1-1.

Figure 1-1 FX5U and Mitsubishi Inverter E700

2. Related Basic Knowledge

The case in this task is based on the application of Mitsubishi FX5U series PLC. Please self-assess if you have the following basics before learning this case. If you are not familiar with the related basic knowledge, please follow the links provided below for preliminary learning.

1. Understanding of communication?

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2. What is serial communication?

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3. Differences between RS232, RS485, and RS422?

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4. What does the communication format include?

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5. What is a communication protocol?

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6. Understanding of RS2 instruction?

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01Hardware Interface

The communication interface standard is the hardware protocol for communication, providing mechanical, electrical, and functional characteristics and regulations. It also defines the connection methods for transmission media and network interfaces, as well as the methods for data sending and receiving. Among serial data interface standards, the most commonly used are RS232, RS422, and RS485 serial interface standards. This case uses the RS485 interface.

02Communication Protocol

The communication protocol mainly looks at the communication format and data format.

(1) Communication Format

In serial asynchronous communication, both parties must uniformly set the method of data transmission, the length of the data being transmitted, the method of verification, and the transmission rate to ensure correct communication between both parties. These parameters that are uniformly set by both parties are called the communication format.

The sender defaults to a logical 1 state.

Before sending data, a logical 0 is first sent to notify the other party to start receiving data.

Start bit: Used to notify the other party to start receiving data.

Data bits: The actual useful information.

Data bits can be 7 or 8 bits, set according to actual needs.

Data bits: Verify whether the data bits are sent correctly.

Can set odd parity, even parity, or no parity.

Setting	Number of data bits set to 1	Parity bit
Odd parity	Odd	0
Even	1
Even parity	Odd	1
Even	0

Stop bit: Marks the end of a character’s transmission, usually the stop bit is a high level.Can set 1 bit or 2 bits. Both parties must be consistent.

(2) Data Format

This case takes Modbus RTU communication as an example.

Modbus RTU communication format:

1 start bit

8 data bits

1 parity bit, none if no parity

1 stop bit (with parity), 2 stop bits (without parity)

Modbus RTU data format

One code corresponds to a set of communication formats.

For example: Address code: 01H, 1 start bit, 8 data bits, odd parity, 1 stop bit, so the address code

0 00000001 0 1

Start bit: 1

Data bit: 00000001

Odd parity, the number of data bits set to 1 is odd: 0

Stop bit: 1

03Common Modbus Function Codes and Functions

04Mitsubishi Inverter Communication Addresses (More can be found in Mitsubishi E700 Application P220)

05Instruction Interpretation

(1) Serial Data Transmission RS2 Instruction Description (Note: When using the instruction, high and low bytes must be reversed)

(2) CRC Instruction

3. Implementation of the Task

This case will explain three aspects: hardware wiring, inverter parameter settings, and PLC software program design.

01Hardware Wiring Diagram

Figure 3-1 Wiring Diagram of FX5U and Mitsubishi Inverter

02Inverter Parameter Settings

Before setting parameters, set the inverter parameters to ALLC and set the parameters to 1 to clear all parameters.

03PLC Software Program Design

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