Limit input text boxes to just 0 or 1

Limit input text boxes to just 0 or 1

I wrote this little script that checks to see that the user entered a 0 or
a 1. If its anything else, it changes it to a 0:
$('.lcdnum1').keyup(function(){
if (!($(this).val()==='0' || $(this).val()==='1')){
$(this).val('0');
}
});
The only thing I don't like about it, is that you see the "bad" character
first. If you type a "x", it briefly shows the "x", then it goes away and
is replaced by a 0.
Here is my test URL that demonstrates what is happening:
http://sterlingmodular.com/test/plan-series-build.asp?console=PLNUno&woodtrim=TOBA&speakerplatform=SPSA&lcd4=1
How can I modify this so that its a little smoother for the user? I.e.,
the "bad" character shouldn't show in the first place. Thank you!