Writing "Hello World" to a USB to serial converter

From Rxtx

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Revision as of 21:04, 28 October 2007

This example shows how write a Java program to write out "Hello World" to a USB to serial converter connected to a Windwos XP computer.

Firstly the USB to serial converter in installed using the manufacturer's instructions. Select My Computer->Properties->Hardware->Device Manager->Ports(COM&LPT)->USB - Serial Comm Port (COM4). This shows that the device was installed as a COM4 port.

Then install Sun's Java software (JDK6 Update 3). The JDK files are placed at C:\Program Files\Java\jdk1.6.0_03\ and the runtime files are placed at C:\Program Files\Java\jre1.6.0_03\. Ensure the System Variable "path" (held in My Computer->properties->Advanced->Environment Varables->System Variables) includes ";C:\Program Files\Java\jdk1.6.0_03\bin" at the end.

Install RxTx. This involves placing rxtxSerial.dll and rxtxParallell.dll in both C:\Program Files\Java\jdk1.6.0_03\jre\bin and C:\Program Files\Java\jre1.6.0_03\bin. It also involves placing RXTXcomm.jar in both C:\Program Files\Java\jdk1.6.0_03\jre\lib\ext and C:\Program Files\Java\jre1.6.0_03\lib\ext.

Put the following file in a folder:

/*
 * @(#)SimpleWrite.java	1.12 98/06/25 SMI
 * 
 * Copyright 2003 Sun Microsystems, Inc. All rights reserved.
 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 * 
 * Sun grants you ("Licensee") a non-exclusive, royalty free, license
 * to use, modify and redistribute this software in source and binary
 * code form, provided that i) this copyright notice and license appear
 * on all copies of the software; and ii) Licensee does not utilize the
 * software in a manner which is disparaging to Sun.
 * 
 * This software is provided "AS IS," without a warranty of any kind.
 * ALL EXPRESS OR IMPLIED CONDITIONS, REPRESENTATIONS AND WARRANTIES,
 * INCLUDING ANY IMPLIED WARRANTY OF MERCHANTABILITY, FITNESS FOR A
 * PARTICULAR PURPOSE OR NON-INFRINGEMENT, ARE HEREBY EXCLUDED. SUN AND
 * ITS LICENSORS SHALL NOT BE LIABLE FOR ANY DAMAGES SUFFERED BY
 * LICENSEE AS A RESULT OF USING, MODIFYING OR DISTRIBUTING THE
 * SOFTWARE OR ITS DERIVATIVES. IN NO EVENT WILL SUN OR ITS LICENSORS
 * BE LIABLE FOR ANY LOST REVENUE, PROFIT OR DATA, OR FOR DIRECT,
 * INDIRECT, SPECIAL, CONSEQUENTIAL, INCIDENTAL OR PUNITIVE DAMAGES,
 * HOWEVER CAUSED AND REGARDLESS OF THE THEORY OF LIABILITY, ARISING
 * OUT OF THE USE OF OR INABILITY TO USE SOFTWARE, EVEN IF SUN HAS BEEN
 * ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.
 * 
 * This software is not designed or intended for use in on-line control
 * of aircraft, air traffic, aircraft navigation or aircraft
 * communications; or in the design, construction, operation or
 * maintenance of any nuclear facility. Licensee represents and
 * warrants that it will not use or redistribute the Software for such
 * purposes.
 */
import java.io.*;
import java.util.*;
import gnu.io.*;

/**
 * Class declaration
 *
 *
 * @author
 * @version 1.10, 08/04/00
 */
public class SimpleWrite {
    static Enumeration	      portList;
    static CommPortIdentifier portId;
    static String	      messageString = "Hello, world!";
    static SerialPort	      serialPort;
    static OutputStream       outputStream;
    static boolean	      outputBufferEmptyFlag = false;
    /**
     * Method declaration
     *
     *
     * @param args
     *
     * @see
     */
    public static void main(String[] args) {
	boolean portFound = false;
	String  defaultPort = "COM4";

	if (args.length > 0) {
	    defaultPort = args[0];
	} 

	portList = CommPortIdentifier.getPortIdentifiers();

	while (portList.hasMoreElements()) {
	    portId = (CommPortIdentifier) portList.nextElement();

	    if (portId.getPortType() == CommPortIdentifier.PORT_SERIAL) {

		if (portId.getName().equals(defaultPort)) {
		    System.out.println("Found port " + defaultPort);

		    portFound = true;

		    try {
			serialPort = 
			    (SerialPort) portId.open("SimpleWrite", 2000);
		    } catch (PortInUseException e) {
			System.out.println("Port in use.");

			continue;
		    } 

		    try {
			outputStream = serialPort.getOutputStream();
		    } catch (IOException e) {}

		    try {
			serialPort.setSerialPortParams(9600, 
						       SerialPort.DATABITS_8, 
						       SerialPort.STOPBITS_1, 
						       SerialPort.PARITY_NONE);
		    } catch (UnsupportedCommOperationException e) {}
	

		    try {
		    	serialPort.notifyOnOutputEmpty(true);
		    } catch (Exception e) {
			System.out.println("Error setting event notification");
			System.out.println(e.toString());
			System.exit(-1);
		    }
		    
		    
		    System.out.println(
		    	"Writing \""+messageString+"\" to "
			+serialPort.getName());

		    try {
			outputStream.write(messageString.getBytes());
		    } catch (IOException e) {}

		    try {
		       Thread.sleep(2000);  // Be sure data is xferred before closing
		    } catch (Exception e) {}
		    serialPort.close();
		    System.exit(1);
		} 
	    } 
	} 

	if (!portFound) {
	    System.out.println("port " + defaultPort + " not found.");
	} 
    } 


}

Note that the third import statement has been changed to be "import gnu.io.*;" rather than the "import javax.comm.*;" that appears in Sun's original version.

Note also that the defaultPort has been set to be COM4.

This Java program can be compiled and run by typing the following at the Command Prompt:

javac SimpleWrite.java
java SimpleWrite

"Hello World" should then appear on the device connected to the serial port, assuming that it has been set up to receive a 9600 baud rate, 8 data bits, 1 stop bit, no parity and no handshaking.