Modbus/TCP by jamod

Question

I have written the following program to understand how to use jamod to access registers. First, I use "Modbus Slave" to simulate a virtual TCP-MODBUS Holding registers. And I use my program with jamod lib to read the holding registers that i just made.

But I got errors below:

Exception in thread "main" java.lang.Error: Unresolved compilation problem: 
        MAX_IP_MESSAGE_LENGTH cannot be resolved or is not a field
        at net.wimpi.modbus.io.ModbusTCPTransport.prepareStreams(ModbusTCPTransport.java:223)
        at net.wimpi.modbus.io.ModbusTCPTransport.setSocket(ModbusTCPTransport.java:79)
        at net.wimpi.modbus.io.ModbusTCPTransport.<init>(ModbusTCPTransport.java:59)
        at net.wimpi.modbus.net.TCPMasterConnection.prepareTransport(TCPMasterConnection.java:104)
        at net.wimpi.modbus.net.TCPMasterConnection.connect(TCPMasterConnection.java:67)
        at test_modbus.main(test_modbus.java:36)

Here is my program

import java.io.*;
import java.lang.*;
import java.net.InetAddress;
import net.wimpi.modbus.Modbus;
import net.wimpi.modbus.io.ModbusTCPTransaction;
import net.wimpi.modbus.msg.WriteCoilRequest;
import net.wimpi.modbus.msg.ReadInputRegistersRequest;
import net.wimpi.modbus.msg.ReadInputRegistersResponse ;
import net.wimpi.modbus.net.TCPMasterConnection;

public class test_modbus {

    public static void main(String args[]) {
        try {
            /* The important instances of the class */
            TCPMasterConnection con = null; // the connection
            ModbusTCPTransaction trans = null; // the transaction
            ReadInputRegistersRequest rreq = null; // the read request
            ReadInputRegistersResponse  rres = null; // the read response
            WriteCoilRequest req = null; // the write request


            /* Variables for storing the parameters */
            InetAddress addr = null; // the slave's address
            int port = 502; // the default port


            // 1. Setup the parameters
            addr = InetAddress.getByName("127.0.0.1"); // ** The address
                                                            // assigned to the
                                                            // module **

            // 2. Open the connection
            con = new TCPMasterConnection(addr);
            con.setPort(port);
            con.connect();
            System.out.println( "--- Message: Line:36 success --- " );
            // ~~~~~~~~~~~~~~~~~~~~ The faulty Read Request ~~~~~~~~~~~~~~~~~~~~
            // 3r. Prepare the READ request
            int k = 4000; 
            rreq = new ReadInputRegistersRequest(k, 2); // Reading 8 bytes (of
                                                        // what??)

            // 4r. Prepare the READ transaction
            trans = new ModbusTCPTransaction(con);
            trans.setRequest(rreq);
            System.out.println( "--- Message: Line:46 success --- " );
            // 5r. Execute the READ transaction
            trans.execute();
            rres = (ReadInputRegistersResponse) trans.getResponse();
            System.out.println("Hex Value of register " + "= "
                    + rres.getHexMessage());

            // ~~~~~~~~~~~~~~~~~~~~ The functional Write Request
            // ~~~~~~~~~~~~~~~~~~~~
            // 3w. Prepare the request
            //req = new WriteCoilRequest(coil, true); // Switching ON the "DO 1"
                                                    // (= address 17)

            // 4w. Prepare the transaction
            trans = new ModbusTCPTransaction(con);
            trans.setRequest(req);

            // 5w. Execute the transaction repeat times
            trans.execute();

            // 6. Close the connection
            con.close();

        } catch (Exception ex) {
            System.out.println("Error");
            ex.printStackTrace();
        }
    }
}

Answer 1

Exception in thread "main" java.lang.Error: Unresolved compilation problem: MAX_IP_MESSAGE_LENGTH cannot be resolved or is not a field

means the compiler can not find the (constant) value MAX_IP_MESSAGE_LENGTH.

at net.wimpi.modbus.io.ModbusTCPTransport.prepareStreams(ModbusTCPTransport.java:223)

means that at line 223 of ModbusTCPTransport.java MAX_IP_MESSAGE_LENGTH is referenced.

The problem is not in your code, but in the compilation of the jamod library. Have you copied the code of jamod to your project or have you included the jamod jar to your classpath? If the first then that is your problem, do the latter (use maven http://mvnrepository.com/artifact/net.wimpi/jamod/1.2).