function blockKeyDown(event) {
	 		
    var keyCode = event.which || event.keyCode;
    
    var touche = String.fromCharCode(keyCode);
                
    var code_input = document.getElementById('code');

    if(code_input.value.length < 6) {
        var caracteres = '0123456789';
                
        if(caracteres.indexOf(touche) >= 0) {
            code_input.value += touche;
        }
    }               
}

function delChars(){
    var code_input = document.getElementById("code");
    for(var i = 0; i < code_input.value.length; i++) {
        if(i > 5){
            code_input.value = code_input.value.substr(0, 6);
        }

    }
}