Hello,

Is it possible to read/write to PLC DB from a VC++ application? If, what API do I use? And does anybody got an example?

Best Regards MrKnowls

hi Mrknowls,yes it is possible,search about WinAC ODK manual..
for a controller example that you can use ,trie WinLC RTX.

Thanks AutoGen,

Do you have any example how to do it?

 Hello Mrknowls,

Mrknowls

Hello,

Is it possible to read/write to PLC DB from a VC++ application? If, what API do I use? And does anybody got an example?

Best Regards MrKnowls

 please provide more details. What are you planing to do?
On which System is the application running?
And which kind of PLC do you want to connect?

This details would be necessary to get a more detailed replay.

Good luck
Sabine

Hello Sabine,

I will develop an VC++ application that will configure an S7-400 PLC (Later an S7-1500) . Write configuration data to DB's and read the corresponding DB's. The application will run on Windows 7.

What is the easiest way to make the connection?

MrKnowls

Introduction

In this article I will explain how to communicate withPLC(Programmable Logic Controller). I started my PLC communication program using .NET from 2007.

For a basic understanding of what PLC is, use Google because basically I am not a PLC Engineer or Electrical Engineer, but I will explain to you how to connect PLC using .NET programs, how to read data from PLC, and how to write data to PLC. My sample programs are all based on MELSEC PLC using TCP/IP communication.

There are different kinds of PLC available like MELSEC ,SIMENS, and etc. For each PLC communication there are different types of protocols available. In this demo program I have used TCP IP communication for MELSEC PLC.

Here I have mentioned .NET programs instead of a language in .NET. In my article you will find four Zip files:

1. SPLCSharpConnect.zipcontains the PLC component DLL source code. I started PLC communication programming in 2007. At that time I was coding using VB.NET. I created my own Winsock component using VB.NET. Even now for PLC communication I am using the same Winsock componentMelsecPLC.dllin my projects. In that component I have created simple functions asConnect,Disconnect,Read,Write, and aDataArrivalevent. In the sample project I have attached I have used the same DLL.

Before we start PLC communication programming, I'd like to explain the read and write processes in PLC communication.

Read Data from PLC

PLC Read Command: To read data from PLC we need to send the command to PLC. Basically the command we send will be like this: "500000FF03FF000018000A04010000D*0095000001";

Stringcmd ="";

cmd = cmd +"5000";//sub HEAD (NOT)

cmd = cmd +"00";//network number (NOT)

cmd = cmd +"FF";//PLC NUMBER

cmd = cmd +"03FF";//DEMAND OBJECT MUDULE I/O NUMBER

cmd = cmd +"00";//DEMAND OBJECT MUDULE DEVICE NUMBER

cmd = cmd +"001C";//Length of demand data

cmd = cmd +"000A";//CPU inspector data

cmd = cmd +"0401";//Read command (to read the data from PLC we should "0401"

cmd = cmd +"0000";//Sub command

cmd = cmd +"D*";//device code

cmd = cmd +"009500";//adBase

cmd = cmd +"0001";

//Device No ,It’s a Address every PLC device will have an address

//we need to send the appropriate address to read the data.

Write Data to PLC

PLC Write Command: To write data to PLC we need to send the command to PLC. Basically the command we send will be like this: "500000FF03FF00001C000A14010000D*0095010002".

Stringcmd ="";

cmd = cmd +"5000";//sub HEAD (NOT)

cmd = cmd +"00";//network number (NOT)

cmd = cmd +"FF";//PLC NUMBER

cmd = cmd +"03FF";//DEMAND OBJECT MUDULE I/O NUMBER

cmd = cmd +"00";//DEMAND OBJECT MUDULE DEVICE NUMBER

cmd = cmd +"001C";//Length of demand data

cmd = cmd +"000A";//CPU inspector data

cmd = cmd +"1401";//Write command

cmd = cmd +"0000";//Sub command

cmd = cmd +"D*";//device code

cmd = cmd +"009501";//adBase

cmd = cmd +"0002";//BASE ADDRESS

You can see the difference, to read we use "0401" and "009500" but for write we use "1401" and "009501". The detailed code will be listed below.

Using the Code

I have attached C# sample programs for PLC communication in this article but for explanation here, Here I have used my componentMelsecPLC.dllin the test project. First addMelsecPLC.dllto your project.

1. Delcare MelsecPLC.dll in the form

//

usingMelsecPLC;

2. Variable declarations

//

publicMelsecPLC.Winsock winsock1;//Declare the MelsecPLC Winsock Component

stringJig01;//To store the PLC read data.

3. Connect (PLC connection)

For connection we need the PLC IP address. Here my PLC IP address is “10.126.224.221”. Enter the local port and remote port. Here I have used “1027” for the local port and “8000” for the remote port. In form load, we call the PLCConnectfunction and we create a MelsecPLCDataArrivalevent. TheDataArrivalevent will be triggered when PLC sends data to the PC (our computer).

The detailed connect functions and DataArrival declaration in the form load are listed below.

privatevoidForm1_Load(objectsender, EventArgs e)

{

winsock1Connect();

winsock1.DataArrival +=

newMelsecPLC.Winsock.DataArrivalEventHandler(winsock1_DataArrival);

timer1.Enabled =true;

timer1.Start();

}

privatevoidwinsock1Connect()

{

try

{

if(winsock1.GetState.ToString() !="Connected")

{

winsock1.LocalPort =1027;

winsock1.RemoteIP ="10.126.224.221";

inta =8000;

winsock1.RemotePort =8000;

winsock1.Connect();

}

}

catch(Exception ex)

{

}

}

4. DataArrival Event

In theDataArrivalevent we get the actual data send by PLC after the Read signal is sent to PLC. This event will be triggered whenever PLC sends data to the PC. To get data from PLC we use thewinsock1.GetData()method.

//

privatevoidwinsock1_DataArrival(MelsecPLC.Winsock sender,intBytesTotal)

{

Strings =String.Empty;

winsock1.GetData(refs);

Jig01 = s;

}

5. Read data from PLC

To read data from PLC we need to send the signal to PLC for data read. I have explained the read functions in my article introduction. To send read signal to PLC, we use thewinsock1.Send()method.

//

privatevoidbtnRead_Click(objectsender, EventArgs e)

{

if(winsock1.GetState.ToString() !="Connected")

{

winsock1Connect();

}

//String cmd = "500000FF03FF000018000A04010000D*0095000001";

Stringcmd ="";

StringOutAddress ="0001";

cmd ="";

cmd = cmd +"5000";//sub HEAD (NOT)

cmd = cmd +"00";//network number (NOT)

cmd = cmd +"FF";//PLC NUMBER

cmd = cmd +"03FF";//DEMAND OBJECT MUDULE I/O NUMBER

cmd = cmd +"00";//DEMAND OBJECT MUDULE DEVICE NUMBER

cmd = cmd +"001C";//Length of demand data

cmd = cmd +"000A";//CPU inspector data

cmd = cmd +"0401";//Read command

cmd = cmd +"0000";//Sub command

cmd = cmd +"D*";//device code

cmd = cmd +"009500";//adBase

cmd = cmd + OutAddress;//BASE ADDRESS

winsock1.Send(cmd);

}

6. Write data to PLC

To write data to PLC we need to send the signal to PLC for data write. I have explained the write functions in my article introduction. To send a write signal to PLC here we use thewinsock1.Send()method.

//

privatevoidbtnWrite_Click(objectsender, EventArgs e)

{

if(winsock1.GetState.ToString() !="Connected")

{

winsock1Connect();

}

Stringcmd ="";

StringOutAddress = txtWrite.Text.Trim();

cmd ="";

cmd = cmd +"5000";//sub HEAD (NOT)

cmd = cmd +"00";//network number (NOT)

cmd = cmd +"FF";//PLC NUMBER

cmd = cmd +"03FF";//DEMAND OBJECT MUDULE I/O NUMBER

cmd = cmd +"00";//DEMAND OBJECT MUDULE DEVICE NUMBER

cmd = cmd +"001C";//Length of demand data

cmd = cmd +"000A";//CPU inspector data

cmd = cmd +"1401";//Write command

cmd = cmd +"0000";//Sub command

cmd = cmd +"D*";//device code

cmd = cmd +"009501";//adBase

cmd = cmd + OutAddress;//BASE ADDRESS

winsock1.Send(cmd);

}