var nav4 = window.Event ? true : false;

function acceptNum(evt){	
	var key = nav4 ? evt.which : evt.keyCode;	
	return (key <= 13 || (key >= 48 && key <= 57));// NOTE: Backspace = 8, Enter = 13, '0' = 48, '9' = 57	
}

function acceptNum_Letras(evt){		
	var key = nav4 ? evt.which : evt.keyCode;	
	return (key <= 13 || (key >= 48 && key <= 57) || (key >= 65 && key <= 90) || (key >= 97 && key <= 122) ); // NOTE: Backspace = 8, Enter = 13, '0' = 48, '9' = 57, A = 65, Z=90,  a=97, z=122
}