Modbus RTU Communication Control between HD700 Frequency Converter and Siemens PLC S7-200

2024-07-26 04:02:57

1 Introduction

Industrial control has moved from stand-alone control to centralized monitoring and distributed control. Today, it has entered the era of network-intensive manufacturing. Industrial controller networking also facilitates network management. Modbus is one of the industrial controller's network protocols. The Modbus protocol is a communication protocol applied to electronic controllers. Through this protocol, controllers can communicate with each other, controllers via a network (such as Ethernet), and other devices. It has become one of the mainstream industry standards. The control equipment produced by different manufacturers conforming to the Modbus protocol can be connected to an industrial network for centralized monitoring.

2. Application Principle of Modbus RTU Protocol in S7-200

2.1 Introduction to the Relationship between Modbus RTU Protocol and S7-200

Siemens developed a command library specifically for Modbus RTU communication, which greatly simplifies the development of Modbus RTU communication and facilitates the rapid implementation of related applications. The Modbus RTU command library enables the S7-200 to be integrated as a master and slave device in a Modbus RTU into a Modbus network for communication between Modbus devices. The following figure shows Micro/WIN's Modbus RTU command library.

Figure 1 Library instructions in the instruction tree

2.2, Modbus RTU master station protocol instruction

The Siemens Modbus Master Protocol Library contains two instructions: the MBUS_CTRL instruction and the MBUS_MSG instruction.

The MBUS_CTRL instruction is used to initialize the master communication. The MBUS_MSG instruction is used to initiate the request to the Modbus slave and process the reply.

The MBUS_MSG instruction is used to initiate a request for a Modbus slave and process the reply.

3, HD700 series inverter Modbus RTU communication

(1) Communication interface

HD700 frequency converter integrates standard RS485 serial communication interface: standard 8-pin RJ45 port; 485 protocol communication terminals A (RS485+), B (RS485?). Both can be used together. A single master/slave or single master/multiple slave control system can be formed. The inverter can only be used as a slave.

(2) Communication

HD700 frequency changer communication agreement is Modbus agreement, RTU message transmission way, supports the common register to read and write. The frame format as shown

Figure 2 Modbus RTU protocol format

Modbus RTU uses the "big-endian" code to represent the address and data items (except for the "little-endian" CRC), which is transmitted first followed by the lower byte.

(3) Command Codes The Modbus RTU protocol supports the following operations.

Table 1 Command Codes

Command code (hexadecimal)

meaning

03H

Read the contents of multiple registers

06H

Modify the contents of a single register. After the inverter is powered off, the modified value is not saved.

10H

Modify the contents of multiple registers. After the inverter is powered off, the modified value is not saved.

17H

Read and modify the contents of multiple registers. After the inverter is powered off, the modified value is not saved.

(3) Mapping between parameter function code and HD700 internal Modbus register

The parameter codes of the HD700 drive are mapped to the Modbus read and write registers. The rules for mapping are:

Parameter function code Ã— 100 = M Ã— 256 + N + 1 Decimal representation, where 0 â‰¤ N â‰¤ 255

High byte low byte Register address

E.g:

Find the Modbus register address of parameter P02.07

2.07 Ã— 100 = 0 Ã— 256 + 206 + 1, then M = 0, N = 206, converted to hexadecimal high byte 00H,

The low byte CEH, the register address is 00CEH. For details, refer to the HD700 User's Manual.

(4) Communication parameters of HD700 inverter

When the HD700 inverter communicates with the host computer, relevant communication parameters need to be set. See Table 2 below.

Table 2 Parameters related to communication of HD700 inverter

Parameter ID

parameter name

Parameter setting range

Defaults

Change way

Modbus address

P00.03

(P10.07)

control method

0: keyboard control

1: Terminal control

2: Communication control

Stop Only

0002H(03EEH)

P00.04

(P01.01)

Given channel

0: Keyboard adjustment

1: UP, DOWN terminal adjustment

2: Multistage speed given

3: AI1 simulation

4: AI2 simulation

5: Serial port communication given

6: DI7 terminal pulse given

7: Bus given

8: Customization given

Run&Stop

0003H(0064H)

P03.27

Communication control word

0ï½ž65535

Run&Stop

0146H

P03.28

Communication control word enable

0ï½ž1

Run&Stop

0147H

P10.02

Local address

0ï½ž247

Run&Stop

03E9H

P10.03

Communication baud rate

0:2.4KBPS

1:4.8KBPS

2:9.6KBPS

3:19.2KBPS

4:38.4KBPS

5:57.6KBPS

Run&Stop

03EAH

P10.04

Communication configuration

0:1-8-1, RTU, no parity

1:1-8-2, RTU, no parity

2:1-8-1, RTU, odd parity

3:1-8-1, RTU, Even Check

Run&Stop

03EBH

P10.05

Native response delay

0ms to 250ms

Run&Stop

03ECH

P10.14

Inverter status word

0ï½ž65535

Actual test value

Actual

03F5H

In the above table, set:

P00.03(P10.07)=2 Communication control inverter.

P00.04(P01.01)=5 The serial communication is selected for the given channel. At this time, the host computer adjusts the given frequency by changing the value of parameter P04.01.

P03.28=1 Enable Communication Control Word

P10.03=3 communication baud rate 19.2KBPS

P10.04=0 Communication configuration 1-8-1, RTU, no parity

P03.27 Communication control word.

The meaning of each bit of this parameter is shown in the table below.

Table 3 Meaning of communication control word P03.27

Bit

Bit function

Inverter prohibited

run

Three-wire mode enable

Forward operation

Reverse running

Forward Reverse

Forward rotation

Reverse rotation

Fault reset

Save parameters

Fault record is cleared

Enable serial port change function selection parameters

Reserved

Refer to the HD700 user manual. The command address for the control word is H0146. Defined by the control word, control the inverter to write H0008 forward, reverse H0010, stop H0000. When writing the frequency, the corresponding register address H0190 (parameter P04.01), the frequency calibration is 1:100.

4, HD700 frequency converter and S7-200 PLC communication wiring

Figure 3 HD700 frequency converter and S7-200 PLC wiring diagram

5, HD700 frequency converter and S7-200 Modbus RTU communication program design

Function: HD700 seven-speed inverter and Siemens S7-200 communication routines (read and write);

Applicable: Siemens S7-200P LC, verified on the CPU 224XP;

Detailed function description: This program is the routine of HD700 frequency converter and S7-200P LC communication to carry out the frequency changer to run, stop control and use the communication to rewrite the setting frequency of the frequency converter and read its running frequency. I0.0 to I0.4 are buttons, where:

I0.0 is the forward rotation control of the inverter

I0.1 is the inverter control

I0.2 is the stop control of the inverter

I0.3 accelerates the inverter

I0.4 is the inverter deceleration

The communication format of this program: baud rate 19200, 1-8-1, RTU, no verification.

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