Si fas clic al botó de sota canvia de valor
<script>
function myFunction()
{
c= document.proves_form.idEntrada.value;
if (c==1)
{
document.proves_form.idEntrada.value = 0 ;
}
else if (c==0)
{
document.proves_form.idEntrada.value = 1 ;
}
}
</script>
<form method="POST" action="" name="proves_form">
<input type= "button" id= "idEntrada" value="0" onclick="myFunction()">
</form>