Question

I was able to make a connection with a PLC to read data from it. Now there’s one problem and it is that I have to write a method to modify the data from the PLC. To achieve this, I have to send two values to the PLC: an int value and a boolean value. I got the int value solved via the classes from the net.wimpi.modbus package. But when it comes to the boolean value I have no clue what to do.

If someone had the same problem as I do now, could you please send me a reference where I can find a solution or a link of a really good tutorial to solve my problem? Someone posted a couple of links in this question but it sends me to tutorials that doesn’t have much to do with the communication with the PLC’s and how to treat the data of the PLC.

EDIT

I made the connection with a Modicon M340 PLC, and for the connection I use the classes of the net.wimpi.modbus package. I made the connection in my code through the classes ModbusTCPTransaction and TCPMasterConnection, and I read the values through the classes ReadMultipleRegistersRequest and ReadMultipleRegistersResponse.

The code I made for the connection:

    private InetAddress m_Address;
private ModbusTCPTransaction m_Transaction = null;
private TCPMasterConnection m_Connection = null;

int port = Modbus.DEFAULT_PORT;
private Activity activity;


public ModbusConnection(Activity activity, String ip)
{
    this.activity = activity;

    try {
        m_Address = InetAddress.getByName(ip); 
    } catch (UnknownHostException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } // the slave'saddress
}

public void getTransaction(InetAddress inet) throws Exception
{
    /*Variables for the reading of the PLC data*/
    int port = Modbus.DEFAULT_PORT;

    /*Data initialization for the reading of the PLC data*/
    m_Connection = new TCPMasterConnection(inet);
    m_Connection.setPort(port);
    m_Connection.connect();
    m_Transaction = new ModbusTCPTransaction(m_Connection);
}

And to read the values, I call the next code all the time. I accomplished only reading and writing int, String and float values through words that I read from an offset declared on the PLC:

    private ReadMultipleRegistersResponse readValues(int offset, int count) 
{
    ReadMultipleRegistersRequest rReq = null; // the request
    ReadMultipleRegistersResponse rRes = null; // the response

    try {

        rReq = new ReadMultipleRegistersRequest(offset, count);
        m_Transaction.setRequest(rReq);
        m_Transaction.execute();
        rRes = (ReadMultipleRegistersResponse) m_Transaction.getResponse();

    } catch (Exception e) {
        e.printStackTrace();
        Log.i("AsyncTask", "doInBackground: Exception");
    }
    return rRes;    
}

EDIT 2

I think I accomplished what I wanted. There are 4 classes that I use to read the coils:

ReadCoilsRequest
ReadCoilsResponse
WriteMultipleCoilsRequest
WriteMultileCoilsResponse

What I did is two methods to read and write coils into the PLC:

    private ReadCoilsResponse readBytes(int offset, int count) 
{
    ReadCoilsRequest rReq = null; // the request
    ReadCoilsResponse rRes = null; // the response

    try {

        rReq = new ReadCoilsRequest(offset, count);
        m_Transaction.setRequest(rReq);
        m_Transaction.execute();
        rRes = (ReadCoilsResponse) m_Transaction.getResponse();

    } catch (Exception e) {
        e.printStackTrace();
        Log.i("AsyncTask", "doInBackground: Exception");
    }
    return rRes;    
}

    public void writeBytes(int wordNumber, BitVector b) {
    try {               
        WriteMultipleCoilsRequest wReq = null; //
        WriteMultipleCoilsResponse wRes = null; //

        wReq = new WriteMultipleCoilsRequest(211, b);
        m_Transaction.setRequest(wReq);
        m_Transaction.execute();    
    } catch (Exception e) {
        e.printStackTrace();
        Log.i("AsyncTask", "doInBackground: Exception");
    }
}

Also, I made a method to read BitVector variables using the Coils classes:

    public BitVector readBitVector(int offset, int count) 
{
    BitVector myBitVector;  

    ReadCoilsResponse rRes = readBytes(offset, count);
    rRes = (ReadCoilsResponse) m_Transaction.getResponse();
    myBitVector = rRes.getCoils();

    return myBitVector; 
}

After this, what I used to set the bit to 1 or 0 is using a native function from the BitVector class from the net.wimpi.modbus.util package in my code:

test.setBit(2, true);

NOTE: It is important to remember that everytime that you want to read or write values to the plc, the best way to do it is opening a closing the connection to the PLC.

Answer 1

My definitive answer is: you have to treat the registers as bits. So if you want to write the second bit of a register represented in an int value in your code, you will have to do something like this:

intValue = m_Data[1].getValue();
intValue = intValue | 2;
m_Data[1].setValue(intValue);

The second line modifies the bit I want to write in my PLC.