Valor PHP en Script

[Death_Empire]

Código PHP:

  <?php
 $piso='';
?>
<script>                                                                     
piso = "<?php echo $piso;?>";
  if(piso == '')     /* Esta comparacion al parecer es el error*/                                    
  {                                                                           
      document.write("<table><tr><td align=center>::. NO EXISTE SELECCION .::</td></tr></table>");              
  }                                                                           
  else                                                                        
  {                                                                           
      document.write("src='../../cgi-bin/condoc.sh?tipo=01&numero=1396568'");
  } 
</script>