 <p>Is that binary or hexadecimal value?</p> <p>Basically it means you have a bus of wires, in which some bits are <code>X</code> (unknown), and others are <code>0</code>.</p> <p>If I saw this binary value: <code>0x0x0x</code>, it would just mean that bits 5,3, and 1 are <code>0</code>, and bits 4,2, and 0 are <code>X</code>.</p>