the output of Counter (digital) is always 'unknown' (2). It should be '0' (3) or '1'(4). So i check the Model, and the problem is at the first JK FilpFlop. But i don't know why the 'Q' output is always 'unknown'.  And I simulation the the counter3 (Counter with 3 bits lang output),the output is all right Hier is the output course of Counter and Counter3.  Can someone tell me, whether the Counter is wrong.