title: RFID's EPC memory private bits meaning
body: <p>I'm reading and writing some RFID, whose EPC is 16 bit long.
  Let's say I write 16 byte <code>00 (0x00)</code> on a tag, and then read the whole EPC memory, which is 20 byte long, I get:</p>
  
  <pre><code>41CB400000000000000000000000000000000000
  </code></pre>
  
  <p>Let's say now I write <code>11223344</code> as new EPC and then I read the memory again, I get:</p>
  
  <pre><code>3658100011223344000000000000000000000000
  </code></pre>
  
  <p>Keep in mind that the maximum length of the EPC byte array that you can write is 16.</p>
  
  <p>Every time I read the memory there are 4 bytes more at the beginning, and I wanted to know what they mean. I think that the 3rd and 4th bytes indicates the length of the EPC: <code>4000 [16384]</code> for the <code>16bit</code>, <code>1000 [4096]</code> for the <code>4bit</code></p>
  
  <p>What does the other mean?</p>