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    <p>Most of devices implement a well known protocol to send data so whoever that is listening and knows this protocol can interpret this data. Tipically they send it in frames (most of times with a fixed length) that has some additional info such as status, data length, data type, etc. For instance something like this:</p> <pre><code>| 0010 | 0001 | 1101 | 0000 ... 0010 1101 | 0111 | status type length data CRC </code></pre> <p>If this is the case you would have to contact the manufacturer to get the protocol documentation.</p> <p>If it's not and this surveillance device is sending data all time then you can do this:</p> <ol> <li>Read this data as bytes.</li> <li>If you receive this pair of bytes: <code>0xFF, 0xD8</code> then you are in presence of a <a href="http://en.wikipedia.org/wiki/JPEG" rel="nofollow">JPEG</a> picture as these bytes are the Start Of Image (SOI) marker. Then next data should be part of the image until you get this pair of bytes: <code>0xFF, 0xD9</code> which are the End Of Image (EOI) marker.</li> <li>If you don't receive this pair, then you can interpret these bytes as text characters </li> </ol> <p>The following examples are taken from official RXTX site and both of them read data as bytes:</p> <ul> <li><p><a href="http://rxtx.qbang.org/wiki/index.php/Two_way_communcation_with_the_serial_port" rel="nofollow">Two way communcation with the serial port</a></p></li> <li><p><a href="http://rxtx.qbang.org/wiki/index.php/Event_based_two_way_Communication" rel="nofollow">Event Based Two Way Communication</a></p></li> </ul>
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