title: What is multiple constant driver error in VHDL
body: <p>I am developing a VHDL program for flash interface. While compiling my program I got this error. </p>
  
  <p><a href="https://i.stack.imgur.com/MgsRA.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/MgsRA.png" alt="enter image description here"></a>
  <em>(clickable)</em></p>
  
  <p>As you can see in the picture, two signals (right hand side) are "xnor" ed and result is assigned to output (flash_oe). </p>
  
  <p>Can anyone describe what is this error message?</p>