URL connection

Hi,

Please go through this document. I hope you will get a good idea.

un's JavaSoft division provides support for RS-232 and parallel devices with standard extensions

The javax.comm API: What is provided

The javax.comm API provides the following functionality to developers:

A complete API specification for serial and parallel communication ports. (In this article we consider serial ports only.) Without a common API in your development efforts, workload will increase

because you'll have to provide support to serial devices.

Full control of all serial framing parameters (baud stop bits, parity, bits/frame) as well as manual or automatic control of the flow control lines. Normally, in RS-232, there are two signal lines

and the rest are intended for control lines. Depending on the type of communication (synchronous or asynchronous), the number of control lines selected may vary. This API provides access to

the underlying control signals.

A brief diversion here may help you understand something about parity and start and stop bits. Parity was added to RS-232 because communication lines can be noisy. Let's say we send ASCII

0, which in hex equals 0x30 (or 00110000 in binary), but along the way someone passes by holding a magnet, causing one of the bits to change. As a result, instead of sending 8 bits as

intended, an additional bit is added to the first string of bits sent, making the sum total of bits sent even or odd. voil! You've got parity.

Start and stop bits were added to the serial communication protocol to allow the receivers to synchronize on the characters being sent. One-bit parity does not allow error correction -- only

detection. Solutions to this problem come from protocols that are layered on top of the serial APIs. Most serial communication these days uses block protocols with checksums (a mathematical

function that can be generated on the receiver and compared to the transmitted checksum) that allow errors to be detected on larger groups of bits. When you are communicating with your ISP

over PPP, packets may be 128 bytes per packet with a checksum. If they match, you are 99.999% sure the data is okay.

There are cases wherein this scheme doesn't work. For example, when sending critical commands to devices that are very far out in the solar system, forward correcting protocols can be used.

Forward correcting protocols are needed because there may be no time for a retransmission, and space has a lot of electromagnetic noise.

Okay, back to the list of functionalities provided by the javax.comm API!

The basic I/O via a subclass of Java IO streams. For input and output, the javax.comm API uses streams; the concept of streams should be familiar to all Java programmers. It is important to

reuse Java concepts when building new functionality or the APIs will become unwieldy.

Streams that can be extended to provide client flow control and threshold controls. For example, you may want an alert when there are 10 characters in the buffer or when there are only 10

locations left for characters. Flow control is important when the two devices connected via an interface cannot keep up with each other. Without flow control, you can have overruns or

underruns. In the overrun condition, you received data before it was processed so it was lost; in the underrun, you were ready for data but it was not available. Usually these conditions occur at

the USART (Universal Synchronous Asynchronous Receiver Transmitter), which is hardware that converts bytes to a serial wave form with timing to match the baud rate.

The javax.comm API uses the Java event model to provide notification of various signal line changes as well as buffer status. State changes refer to well-defined signals specified in the RS-232

standard. For example, carrier detect is used by a modem to signal that it has made a connection with another modem, or it has detected a carrier tone. Making the connection or detecting a

carrier tone is an event. Event detection and notification of changes is implemented in this API.

What is not provided

The javax.comm API does not provide:

Line discipline type processing, dialer management, or modem management. Line discipline refers to additional processing of input or output characters. For example, one common

post-processing option is the conversion of CR to CR LF. These terms have their origins in the early days of teletypes. CR (carriage return) means to simple-return the carriage to the left

margin; in the Arabic world, this would be the right margin. LF (line feed) advances the printing area up by one. When bitmap screens and laser printers came along, these terms became less

important.

Dialer management and modem management are additional applications that can be written using the javax.comm API. Dialer management typically provides an interface to the modem

management's AT command interface. Almost all modems have an AT command interface. This interface is documented in modem manuals.

Perhaps a little example will make this concept clear. Suppose we have a modem on COM1 and we want to dial a phone number. A Java dialer management application will query for the

phone number and interrogate the modem. These commands are carried by javax.comm, which does no interpretation. To dial the number 918003210288, for example, the dialer management

probably sends an "AT," hoping to get back an "OK," followed by ATDT918003210288. One of the most important tasks of dialer management and modem management is to deal with errors

and timeouts.

GUI for serial port management. Normally, serial ports have a dialog box that configures the serial ports, allowing users to set parameters such as baud rate, parity, and so on. The following

diagram depicts the objects involved in reading and/or writing data to a serial port from Java.

Support for X, Y, and Z modem protocols. These protocols provide support error detection and correction.

The programming basics

Too often, programmers dive right into a project and code interactively with an API on the screen without giving any thought to the problem they are trying to solve. To avoid confusion and potential

problems, gather the following information before you start a project. Remember, programming devices usually requires that you consult a manual.

1.Get the manual for the device and read the section on the RS-232 interface and RS-232 protocol. Most devices have a protocol that must be followed. This protocol will be carried by the

javax.comm API and delivered to the device. The device will decode the protocol, and you will have to pay close attention to sending data back and forth. Not getting the initial set-up correct

can mean your application won't start, so take the time to test things out with a simple application. In other words, create an application that can simply write data onto the serial port and

then read data from the serial port using the javax.comm API.

2.Try to get some code samples from the manufacturer. Even if they are in another language, these examples can be quite useful.

3.Find and code the smallest example you can to verify that you can communicate with the device. In the case of serial devices, this can be very painful -- you send data to a device connected to

the serial port and nothing happens. This is often the result of incorrect conditioning of the line. The number one rule of device programming (unless you are writing a device driver) is to make

sure you can communicate with the device. Do this by finding the simplest thing you can do with your device and getting that to work.

4.If the protocol is very complicated, consider getting some RS-232 line analyzer software. This software allows you to look at the data moving between the two devices on the RS-232

connection without interfering with the transmission.

Using the javax.comm API successfully in an application requires you to provide some type of interface to the device protocol using the serial API as the transport mechanism. In other words, with the

exception of the simplest devices, there is usually another layer required to format the data for the device. Of course the simplest protocol is "vanilla" -- meaning there is no protocol. You send and

receive data with no interpretation.

Overview of suggested steps for using javax.comm

In addition to providing a protocol, the ISO layering model used for TCP/IP also applies here in that we have an electrical layer, followed by a very simple byte transport layer. On top of this byte

transport layer you could put your transport layer. For example, your PPP stack could use the javax.comm API to transfer bytes back and forth to the modem. The role of the javax.comm layer is quite

small when looked at in this context:

1.Give the javax.comm API control of some of the devices. Before you use a device, the javax.comm API has to know about it.

2.Open the device and condition the line. You may have a device that requires a baud rate of 115 kilobits with no parity.

3.Write some data and/or read data following whatever protocol the device you are communicating with requires. For example, if you connect to a printer, you may have to send a special code to

start the printer and/or end the job. Some PostScript printers require you to end the job by sending CTRL-D 0x03.

4.Close the port.

Initializing the javax.comm API registry with serial interface ports

The javax.comm API can only manage ports that it is aware of. The latest version of the API does not require any ports to be initialized. On start-up, the javax.comm API scans for ports on the

particular host and adds them automatically.

You can initialize the serial ports your javax.comm API can use. For devices that do not follow the standard naming convention, you can add them explicitly using the code segment below.

// Register the device

CommPort ttya = new javax.comm.solaris.SolarisSerial("ttya","/dev/ttya");

CommPortIdentifier.addPort(ttya,CommPortIdentifier.PORT_SERIAL);

CommPort ttyb = new javax.comm.solaris.SolarisSerial("ttyb","/dev/ttyb");

CommPortIdentifier.addPort(ttyb,CommPortIdentifier.PORT_SERIAL);

Opening and conditioning devices

This next code sample demonstrates how to add, condition, and open a device. Details on the specific method calls are in the API pages for javax.comm. This example sets the device called

XYZSerialDevice to be accessible with name GenericSerialReader. The device connected on this line has a baud rate of 9600, 1 stop bit, a character of 8 bits (yes, they can be smaller), and no parity.

The result of all of this is to provide two streams -- one for reading and another for writing.

InputStream input = null;

OutputStream output;

SerialPort serialPort = null;

public GenericSerialReader(String name, int baud,

int timeout) throws Exception {

CommPortIdentifier portId =

CommPortIdentifier.getPortIdentifier( name );

serialPort = (SerialPort)portId.openPort

( "GenericSerialReader", timeout );

serialPort.setSerialPortParams(9600, SerialPort.DATABITS_8,

SerialPort.STOPBITS_1,

SerialPort.PARITY_NONE); //

serialPort.setFlowcontrolMode( SerialPort.FLOWCTRL_NONE ); //

serialPort.enableRcvThreshold ( 1 );

serialPort.enableRcvTimeout ( timeout );

int rosStatus = 0;

System.out.println("Open device called");

output = serialPort.getOutputStream();

input = serialPort.getInputStream();

Writing and reading data

For javax.comm, this is no different than any other read and write method call to the derived output stream.

For write:

try {

output.write ( outputArray, 0 , length );

For read:

try {

int b = input.read()

Closing the port

Closing the port with javax.comm is no different than with other requests to close a device. This step is very important to javax.comm because it attempts to provide exclusive access. Multiplexing

multiple users on a serial line requires a Multiplexor protocol.

try {

inout.close();

output.close();

} ...

Additional example

A good example also is available when you download the javax.comm API package from the Java Developer Connection (see Resources section).

Interfacing a serial device driver to javax.comm

You just picked up this little computer that runs Java and has serial ports. However, the manufacturer has not provided an implementation. It did give you manuals about some calls you could make

via native methods to access the serial port drivers written in C. But how do you interface it to javax.comm so you can use your special hardware device? You guessed it: Implement an interface that

interfaces to the native methods.

The file SerialPort.java, which is included with the javax.comm API, expects that there will be other classes that realize the implementation of the abstract methods declared by SerialPort. In our

example, we call the implementation SolarisSerial.java. This class requires the following native methods to implement the abstract methods called for in CommPort.java and SerialPort.java:

private native int openNativePort( ... )

private native void closeNativePort( ... )

private native int read( ... )

private native int write( ... )

private native byte readByte( ... )

private native void writeByte( ... )

private native void setNativeSerialPortParams( ... )

private native int getStatusFlags( ... )

public void setDTR( ... )

public native void nativeSetDTR( ... )

public void setRTS( ... )

public native void nativeSetRTS( ... )

private native void nativeSendBreak(...)

public native void setRcvFifoTrigger(...)

To support the javax.comm API on a system that currently does not have support, we need to provide implementations for all the methods mentioned above.

Conceptually, we have to provide resource management via open and close; ability to configure and query the port via the set and get methods; and, most importantly, the ability to read and write

bytes to the port. In many cases, the above methods are almost one-to-one mappings to the underlying native operating system. The following table lists the functions used on Solaris to implement

the native interface layer.

javax.comm native method call

Unix OS mappings for javax.comm

private native int openNativePort( ... )

Open

private native void closeNativePort( ... )

Close

private native int read( ... )

Read

private native int write( ... )

Write

private native byte readByte( ... )

Read

private native void writeByte( ... )

Write

private native void setNativeSerialPortParams( ... )

Termio/ioctl

private native int getStatusFlags( ... )

Termio/ioctl

public void setDTR( ... )

Termio/ioctl

public native void nativeSetDTR( ... )

Termio/ioctl

public void setRTS( ... )

Termio/ioctl

public native void nativeSetRTS( ... )

Termio/ioctl

private native void nativeSendBreak(...)

Termio/ioctl

public native void setRcvFifoTrigger(...)

Termio/ioctl

Conclusion

The javax.comm API provides a modern disciplined approach to serial communications and will move Java into new application spaces, allowing devices like bar code scanners, printers, smart card

readers, and hundreds of other serial devices to be connected with ease. The API is easy to use, as demonstrated by the example. It is also easy to port to new hardware platforms. The API has not

been tested for high data rate and realtime applications; therefore, developers looking to use the API in those types of environments should perform careful instrumentation with subsequent analysis

of the code.

In determining whether the API is suitable for high data rate or mission sensitive applications, look for the following:

Characters lost on input

Characters lost in output

Frequency of flow control

Time it takes to deliver an event

Character processing times

Block processing times

When we first started our series on smart cards, we were lucky if we understood a few native method calls to send bytes to serial devices. We end our smart card series with this article. The software

APIs we have been discussing in this series come together from a device point of view. For example, a user developing an application for smart cards can write to some well-defined APIs such as

OpenCard Framework or communicate directly using javax.comm -- or alternatively use javax.smartcard, which in turn uses javax.comm.

The javax.comm API facilitates the interfacing of serial and parallel devices to Java. For more information on how javax.comm works with smart cards, look at the iButtons article. Also, we have

included several examples in the Resources section to get you started.

I hope this will help you.

Thanks

Bakrudeen

bakrudeen_indts at 2007-6-29 3:14:28 >

i am sory this only works if i am in the same local network with the owner of the IP

i am tring to do something like scan ip

gets to ip and scans all the ips between them.

if any computer between these ip s has a shared folder it shows the computer in a tree view

i am using awt not swing so if any one want to help give me hints about awt please

98028140 at 2007-6-29 3:14:28 >