<script type="text/javascript">
$(document).ready(function(){
 $(document).keydown(function(event){
  if(event.keyCode==13){
   var id=$("input:focus").attr("id"); 
   switch(id){
    case "keyword":
     SearchFunction(); 
     break;
    case "...":
     AnyFunction();
     break;
   }
  }
  });
 });
</script>

<input type="text" id="a1" /><input type="button" value="A" /><br />
<input type="text" id="a2" />