function saber(oCntrl){
dias=[0,31,29,31,30,31,30,31,31,30,31,30,31];
ultimo=0;
//document.form1.select1.options[document.form1.select1.selectedIndex].value
var mes=document.frm.mes.options[document.frm.mes.selectedIndex].value;
var exd2 = new Date();
var year2=exd2.getFullYear();

var oyear2=year2;

if (mes==2){
fecha=new Date(oyear2,1,29)
vermes=fecha.getMonth();
if(vermes!=mes){ultimo=28}
}
if(ultimo==0){ultimo=dias[mes]}
//alert("ese mes tiene "+ultimo+" días");
cambia(oCntrl,ultimo);
}


function addOpt(oCntrl, iPos, sTxt, sVal){ 
     var selOpcion=new Option(sTxt, sVal); 
     eval(oCntrl.options[iPos]=selOpcion); 
   } 
 
   function cambia(oCntrl,ultimo){ 
   var mes=ultimo;
    while (oCntrl.length) oCntrl.remove(0); 
    switch (mes){ 
     case 30:
	  addOpt(oCntrl,  00, ".: Dia :.", ".: Dia :."); 
      addOpt(oCntrl,  01, "01", "01"); 
      addOpt(oCntrl,  02, "02", "02"); 
      addOpt(oCntrl,  03, "03", "03"); 
	  addOpt(oCntrl,  04, "04", "04"); 
      addOpt(oCntrl,  05, "05", "05"); 
      addOpt(oCntrl,  06, "06", "06"); 
	  addOpt(oCntrl,  07, "07", "07"); 
      addOpt(oCntrl,  08, "08", "08"); 
      addOpt(oCntrl,  09, "09", "09"); 
	  addOpt(oCntrl,  10, "10", "10"); 
      addOpt(oCntrl,  11, "11", "11"); 
      addOpt(oCntrl,  12, "12", "12"); 
	  addOpt(oCntrl,  13, "13", "13"); 
      addOpt(oCntrl,  14, "14", "14"); 
      addOpt(oCntrl,  15, "15", "15"); 
	  addOpt(oCntrl,  16, "16", "16"); 
      addOpt(oCntrl,  17, "17", "17"); 
      addOpt(oCntrl,  18, "18", "18"); 
	  addOpt(oCntrl,  19, "19", "19"); 
      addOpt(oCntrl,  20, "20", "20"); 
      addOpt(oCntrl,  21, "21", "21"); 
	  addOpt(oCntrl,  22, "22", "22"); 
      addOpt(oCntrl,  23, "23", "23"); 
      addOpt(oCntrl,  24, "24", "24"); 
	  addOpt(oCntrl,  25, "25", "25"); 
      addOpt(oCntrl,  26, "26", "26"); 
      addOpt(oCntrl,  27, "27", "27"); 
	  addOpt(oCntrl,  28, "28", "28"); 
      addOpt(oCntrl,  29, "29", "29"); 
      addOpt(oCntrl,  30, "30", "30");
      break; 
     case 31:
	  addOpt(oCntrl,  00, ".: Dia :.", ".: Dia :."); 
      addOpt(oCntrl,  01, "01", "01"); 
      addOpt(oCntrl,  02, "02", "02"); 
      addOpt(oCntrl,  03, "03", "03"); 
	  addOpt(oCntrl,  04, "04", "04"); 
      addOpt(oCntrl,  05, "05", "05"); 
      addOpt(oCntrl,  06, "06", "06"); 
	  addOpt(oCntrl,  07, "07", "07"); 
      addOpt(oCntrl,  08, "08", "08"); 
      addOpt(oCntrl,  09, "09", "09");
	  addOpt(oCntrl,  10, "10", "10"); 
      addOpt(oCntrl,  11, "11", "11"); 
      addOpt(oCntrl,  12, "12", "12"); 
	  addOpt(oCntrl,  13, "13", "13"); 
      addOpt(oCntrl,  14, "14", "14"); 
      addOpt(oCntrl,  15, "15", "15"); 
	  addOpt(oCntrl,  16, "16", "16"); 
      addOpt(oCntrl,  17, "17", "17"); 
      addOpt(oCntrl,  18, "18", "18"); 
	  addOpt(oCntrl,  19, "19", "19"); 
      addOpt(oCntrl,  20, "20", "20"); 
      addOpt(oCntrl,  21, "21", "21"); 
	  addOpt(oCntrl,  22, "22", "22"); 
      addOpt(oCntrl,  23, "23", "23"); 
      addOpt(oCntrl,  24, "24", "24"); 
	  addOpt(oCntrl,  25, "25", "25"); 
      addOpt(oCntrl,  26, "26", "26"); 
      addOpt(oCntrl,  27, "27", "27"); 
	  addOpt(oCntrl,  28, "28", "28"); 
      addOpt(oCntrl,  29, "29", "29"); 
      addOpt(oCntrl,  30, "30", "30");
	  addOpt(oCntrl,  31, "31", "31");
      break; 
     case 28:
	  addOpt(oCntrl,  00, ".: Dia :.", ".: Dia :."); 
      addOpt(oCntrl,  01, "01", "01"); 
      addOpt(oCntrl,  02, "02", "02"); 
      addOpt(oCntrl,  03, "03", "03"); 
	  addOpt(oCntrl,  04, "04", "04"); 
      addOpt(oCntrl,  05, "05", "05"); 
      addOpt(oCntrl,  06, "06", "06"); 
	  addOpt(oCntrl,  07, "07", "07"); 
      addOpt(oCntrl,  08, "08", "08"); 
      addOpt(oCntrl,  09, "09", "09"); 
	  addOpt(oCntrl,  10, "10", "10"); 
      addOpt(oCntrl,  11, "11", "11"); 
      addOpt(oCntrl,  12, "12", "12"); 
	  addOpt(oCntrl,  13, "13", "13"); 
      addOpt(oCntrl,  14, "14", "14"); 
      addOpt(oCntrl,  15, "15", "15"); 
	  addOpt(oCntrl,  16, "16", "16"); 
      addOpt(oCntrl,  17, "17", "17"); 
      addOpt(oCntrl,  18, "18", "18"); 
	  addOpt(oCntrl,  19, "19", "19"); 
      addOpt(oCntrl,  20, "20", "20"); 
      addOpt(oCntrl,  21, "21", "21"); 
	  addOpt(oCntrl,  22, "22", "22"); 
      addOpt(oCntrl,  23, "23", "23"); 
      addOpt(oCntrl,  24, "24", "24"); 
	  addOpt(oCntrl,  25, "25", "25"); 
      addOpt(oCntrl,  26, "26", "26"); 
      addOpt(oCntrl,  27, "27", "27"); 
	  addOpt(oCntrl,  28, "28", "28"); 
      break;  
	  case 29:
	  addOpt(oCntrl,  00, ".: Dia :.", ".: Dia :."); 
      addOpt(oCntrl,  01, "01", "01"); 
      addOpt(oCntrl,  02, "02", "02"); 
      addOpt(oCntrl,  03, "03", "03"); 
	  addOpt(oCntrl,  04, "04", "04"); 
      addOpt(oCntrl,  05, "05", "05"); 
      addOpt(oCntrl,  06, "06", "06"); 
	  addOpt(oCntrl,  07, "07", "07"); 
      addOpt(oCntrl,  08, "08", "08"); 
      addOpt(oCntrl,  09, "09", "09");
	  addOpt(oCntrl,  10, "10", "10"); 
      addOpt(oCntrl,  11, "11", "11"); 
      addOpt(oCntrl,  12, "12", "12"); 
	  addOpt(oCntrl,  13, "13", "13"); 
      addOpt(oCntrl,  14, "14", "14"); 
      addOpt(oCntrl,  15, "15", "15"); 
	  addOpt(oCntrl,  16, "16", "16"); 
      addOpt(oCntrl,  17, "17", "17"); 
      addOpt(oCntrl,  18, "18", "18"); 
	  addOpt(oCntrl,  19, "19", "19"); 
      addOpt(oCntrl,  20, "20", "20"); 
      addOpt(oCntrl,  21, "21", "21"); 
	  addOpt(oCntrl,  22, "22", "22"); 
      addOpt(oCntrl,  23, "23", "23"); 
      addOpt(oCntrl,  24, "24", "24"); 
	  addOpt(oCntrl,  25, "25", "25"); 
      addOpt(oCntrl,  26, "26", "26"); 
      addOpt(oCntrl,  27, "27", "27"); 
	  addOpt(oCntrl,  28, "28", "28"); 
      addOpt(oCntrl,  29, "29", "29"); 
      break;
    } 
   }