title: VHDL <b_Off_OBUF> is incomplete. The signal is not driven by any source pin in the design
body: <p>I'm trying to write a very simple program on a Spartan-3E development board. I want to read the slide switches and use the LED next to the slide switches to indicate which switch is in the on position.</p>
  
  <p>Here is my code:</p>
  
  <pre><code>library IEEE;
  use IEEE.STD_LOGIC_1164.ALL;
  
  
  entity Switch is
     PORT(a,b,c,d: IN std_logic; 
       a_ON,a_Off,b_ON,b_Off,c_ON,c_Off,d_ON,d_Off: OUT std_logic);
  end Switch;
  
  architecture Behavioral of Switch is
  
  begin
    PROCESS (a)
    begin
      if a = '1' then
        a_ON &lt;= '1';
      else 
        a_OFF &lt;= '1';
      end if;
   END PROCESS;   
  end Behavioral;
  </code></pre>
  
  <p>Here is my *.ucf file:</p>
  
  <pre><code>NET "a" LOC = "L13" | IOSTANDARD = LVTTL | PULLUP ;
  NET "b" LOC = "L14" | IOSTANDARD = LVTTL | PULLUP ;
  NET "c" LOC = "H18" | IOSTANDARD = LVTTL | PULLUP ;
  NET "d" LOC = "N17" | IOSTANDARD = LVTTL | PULLUP ;
  
  NET "d_OFF" LOC = "F9" | IOSTANDARD = LVTTL | SLEW = SLOW | DRIVE = 8 ;
  NET "d_ON" LOC = "E9" | IOSTANDARD = LVTTL | SLEW = SLOW | DRIVE = 8 ;
  NET "c_OFF" LOC = "D11" | IOSTANDARD = LVTTL | SLEW = SLOW | DRIVE = 8 ;
  NET "c_ON" LOC = "C11" | IOSTANDARD = LVTTL | SLEW = SLOW | DRIVE = 8 ;
  NET "b_OFF" LOC = "F11" | IOSTANDARD = LVTTL | SLEW = SLOW | DRIVE = 8 ;
  NET "b_ON" LOC = "E11" | IOSTANDARD = LVTTL | SLEW = SLOW | DRIVE = 8 ;
  NET "a_OFF" LOC = "E12" | IOSTANDARD = LVTTL | SLEW = SLOW | DRIVE = 8 ;
  NET "a_ON" LOC = "F12" | IOSTANDARD = LVTTL | SLEW = SLOW | DRIVE = 8 ;
  </code></pre>
  
  <p>Here is the errors I get:</p>
  
  <blockquote>
    <p>PhysDesignRules:368 - The signal  is incomplete. The signal
    is not driven by any source pin in the design.</p>
    
    <p>ERROR:PhysDesignRules:368 - The signal  is incomplete. The
    signal is not driven by any source pin in the design.</p>
    
    <p>ERROR:PhysDesignRules:368 - The signal  is incomplete. The
    signal is not driven by any source pin in the design.</p>
    
    <p>ERROR:PhysDesignRules:368 - The signal  is incomplete. The
    signal is not driven by any source pin in the design.</p>
    
    <p>ERROR:PhysDesignRules:368 - The signal  is incomplete. The
    signal is not driven by any source pin in the design.</p>
    
    <p>ERROR:PhysDesignRules:368 - The signal  is incomplete. The
    signal is not driven by any source pin in the design.</p>
    
    <p>WARNING:PhysDesignRules:367 - The signal  is incomplete. The
    signal does not drive any load pins in the design.</p>
    
    <p>WARNING:PhysDesignRules:367 - The signal  is incomplete. The
    signal does not drive any load pins in the design.</p>
    
    <p>WARNING:PhysDesignRules:367 - The signal  is incomplete. The
    signal does not drive any load pins in the design.</p>
    
    <p>WARNING:PhysDesignRules:367 - The signal  is incomplete. The
    signal does not drive any load pins in the design.</p>
  </blockquote>