Serial Programming - upload.wikimedia....

JavaComm API
6.2.4 Simple Data Transfer
Simple Writing of Data
Writing to a serial port is as simple as basic Java IO. However there are a couple of caveats
to look out for if you are using the AT Hayes protocol:
1. Don't use println (or other methods that automatically append "\n") on the OutputStream.
The AT Hayes protocol for modems expects a "\r\n" as the delimiter
(regardless of underlying operating system).
2. After writing to the OutputStream, the InputStream buffer will contain a repeat of
the command that was sent to it (with line feed), if the modem is set to echoing the
command line, and another line feed (the answer to the "AT" command). So as part
of the write operation make sure to clean the InputStream of this information (which
can actually be used for error detection).
3. When using a Reader/Writer (not a really good idea), at least set the character
encoding to US-ASCII instead of using the platform's default encoding, which might
or might not work.
4. Since the main operation when using a modem is to transfer data unaltered, the
communication with the modem should be handled via InputStream/OutputStream,
and not a Reader/Writer.
// Write to the output
os.print("AT");
os.print("\r\n"); // Append a carriage return with a line feed
is.readLine(); // First read will contain the echoed command you
sent to it. In this case: "AT"
is.readLine(); // Second read will remove the extra line feed that
AT generates as output
Simple Reading of Data (Polling)
If you correctly carried out the write operation (see above) then the read operation is as
simple as one command:
// Read the response
String response = is.readLine(); // if you sent "AT" then response
== "OK"
Problems with the simple Reading / Writing
The simple way of reading and/or writing from/to a serial port as demonstrated in the
previous sections has serious drawbacks. Both activities are done with blocking I/O. That
means, when there is
• no data available for reading, or
• the output buffer for writing is full (the device does not accept (any more) data),
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