<input type="text" maxlength="6" placeholder="Zip/Postal Code*" class="input-text required-entry validate-length maximum-length-6 minimum-length-6 validate-digits" value="" id="billing:postcode" name="billing[postcode]" title="Pincode">
if you want to use any number of integer validation on input filed use this 2 syntax.
maxlength=”6″
class=”input-text required-entry validate-length maximum-length-6 minimum-length-6 validate-digits”
