See the RxTx installation instruction for details. This API is not part of the standard Java 2 version. Instead, an implementation of the API has to be downloaded separately.
Unfortunately, JavaComm has not received much attention from Sun, and hasn't been really maintained for a long time. From time to time Sun does trivial bug-fixes, but doesn't do the long overdue main overhaul. The provided source code is kept simple to demonstrate important point. It needs to be enhanced when used in a real application. The source code in this chapter is not the only available example code. The JavaComm download comes with several examples.
Unfortunately, Sun does not provide any real tutorial or some introductory text. Therefore, it is worth studying the example code to understand the mechanisms of the API. Still, the API documentation should be studied, too. But the best way is to study the examples and play with them.
Due to the lack of easy-to-use application and people's difficulty in understanding the APIs programming model, the API is often bad-mouthed. The API is better than its reputation, and functional. But no more. The API uses a callback mechanism to inform the programmer about newly arriving data. It is also a good idea to study this mechanism instead of relying on polling the port.
Unlike other callback interfaces in Java e. If multiple listeners require to listen to serial events, the one primary listener has to be implemented in a way that it dispatches the information to other secondary listeners. Under this location Sun currently provides JavaComm 3.
Downloading requires to have registered for a Sun Online Account. The download page provides a link to the registration page. The purpose of this registration is unclear. One can download JDKs and JREs without registration, but for the almost trivial JavaComm Sun cites legal and governmental restrictions on the distribution and exportation of software. The Windows version of JavaComm is no longer officially available, and Sun has - against their own product end-of-live policy - not made it available in the Java products archive.
However, the 2. Installation Follow the installation instructions that come with the download. Some versions of JavaComm 2. The most obvious of the two instructions is unfortunately the wrong one, intended for ancient Java 1. The information referring to the also ancient Java 1.
Particularly Windows users are typically not aware that they have copies of the same VM installed in several locations typically three to four. The installation needs to be repeated for every VM installation JDKs and JREs which should be used in conjunction with the development and execution of a serial application. Often a library like JavaComm not only needs to be made known to the IDE as such, but also to each project that is supposed to use the library. Read the IDE's documentation.
It should be noted that the old JavaComm 2. In such a case an external browser is needed to read the documentation a recommended activity Initially I looked for an unencumbered free Serial IO library. They were fine for developing the application, and in initial testing, but in production they each proved unstable. Converting over was literally an exercise in changing imports, and the library has been absolutely rock solid - I cannot recommend it enough. Lastly, their licensing is pretty darn reasonable as long as you are not preinstalling software on the equipment for your customer s.
From the other side, if you want to do it using C , which will run on both Windows and Linux--with some limitations EDIT: which may be out of date. I have no way to test it. Just create a SerialPort object, set its baudrate, port and any other odd settings, call open on it, and write out your byte[]s. After all the setup, the SerialPort object acts very similar to any networked stream, so it should be easy enough to figure out.
And as ibrandy states, you need to know all these settings, like baud rate, before you even start attempting to communicate to any serial device. At work we use teraterm and realterm for checking serial data is correctly formatted. Also we have a hardware splitter with a switch so we can monitor traffic to our application via a cable back to another port.
Windows allows you access to the serial port via CreateFile. That gives you a handle and from there you can configure access. Depending on the device You are trying to communicate with, there may be more parameters than the baud rate, number of data bits, type of parity checking and number of stop bits to consider. If I recall correctly, modems use nine lines of the RSC interface.
In general it's good to know how the interface works. You can't communicate if the baud rate doesn't match, but wrong setting of other parameters might kind of work. For example You can easily send data to the device expecting 1 stop bit with 2 stop bits set. Problems start when You try to receive data in such case.
You can also use appropriately set parity bit as one of stop bits, etc. If you are not forced to use a particular compiler I suggest to use Qt and in the new 5. The code you will write will run on all supprited Qt platforms, at least those that have serial ports. 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. Using the javax. 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. On top of this byte transport layer you could put your transport layer. For example, your PPP stack could use the javax. The role of the javax. Give the javax. Before you use a device, the javax. Open the device and condition the line. You may have a device that requires a baud rate of kilobits with no parity.
The latest version of the API does not require any ports to be initialized. On start-up, the javax. You can initialize the serial ports your javax. For devices that do not follow the standard naming convention, you can add them explicitly using the code segment below.
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. The device connected on this line has a baud rate of , 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. Here are the latest Insider stories. More Insider Sign Out. Sign In Register. Sign Out Sign In Register. Latest Insider. Check out the latest Insider stories here. More from the IDG Network. What is an API? Issues, like timing, noise, and the fundamentally analog nature of electronics have to be considered. Therefore, theres a host of layered protocols so that the receiving end can recognize when data is being sent, whether the data was received correctly, and more.
Serial communication uses some very basic, simple protocols. Sending between 3 and 15 volts across the serial cable for a number of nanoseconds inversely proportional to the baud rate of the connection is a zero bit. Sending between -3 and volts for the same amount of time is a one bit. Sending between 3 and -3 volts is a hardware error.
These bits are grouped into serial data units, SDUs for short. Most modern devices use eight data bits per SDU. However, some older devices use seven, six, or even five data bits per SDU. However, there may be gaps of indeterminate length between SDUs. One of the problems faced by asynchronous serial devices is determining SDU boundaries.
If a modem receives eight data bits, how is it to tell whether thats an entire SDU or the last four bits of one SDU and the first four bits of another, especially if the connection has some noise and isn particularly reliable? To assist with this, each SDU is preceded by a single start bit thats always 0, and followed by between one and two stop bits.
Stop bits last longer than data bits so they can always be identified. In addition to the data and the start and stop bits, an SDU may have a parity bit. Parity is a very simple error detection scheme that can detect but not correct single bit errors in an SDU. There are two basic parity schemes. Even parity adds an extra one bit to the end of the SDU if there are an even number of one bits in the data.
Odd parity adds an extra one bit to the end of the SDU if there are an odd number of one bits in the data. The combination of data bits, parity scheme, and stop bits is abbreviated in forms like 8N1 or 7E1. Virtually all modern systems use 8N1.
Mark parity always adds a one bit for the parity; space parity always adds a zero bit. These convey no useful information and are almost never used. The baud rate is the number of times per second the state of the communication channel changes.
This is not the same as bits per second. Modern modems send multiple bits per baud. Most U. Modems that send higher bit rates send multiple bits with each baud. A 28, bps modem is a baud modem with nine states, for example. The Java Communications API lets you set all of these parameters, including baud rate, data bits, stop bits, and parity. They should all be familiar to anyone whos struggled with modem init strings and terminal software in the bad old days before the Internet separated connectivity from content.
Four methods in the SerialPort class return the values of these settings. They are:. A little surprisingly, you can set these values independently. Instead, all four values baud, data bits, stop bits, and parity are set at once with the setSerialPortParams method:.
If the requested values are not supported by the driver e. Except for the baud rate, these arguments should be one of several mnemonic constants in the SerialPort class:.
0コメント