help about cycloneII!!!!

The PLL_OUTn pins can either be the negative pin for a differential pair if the clock output is using a differential I/O standard. If not then it can only be used as a regular I/O pin. This pin still needs to follow all of the other pin placement rules due to current strength and switching noise. Check to see if you are following the pin placement guidelines in the handbook for I/O pins. Also when it "isn't working", check to see if you are getting any error messages for a clue on why it isn't compiling. It could be an I/O placement rule was violated.