product listing with ajax

HI.

I gonna load the products through ajax in Joomla. I know it is not part of the code, but I'm developer, so maybe a little advice help me.

I chreated a template without any content just this:
<?php if($this->countModules('ajax')) : ?>
<div class="ajax-xhr-load">
<jdoc:include type="modules" name="ajax" style="none" />
</div>
<?php endif; ?>

After I created a menu item, and set the type to "Hikashop -> product listing"
set template to ajax
I binded a module for it "Associated product for category listing module 142"
The position of the module is "ajax"

So if I open it in the browser this will call the product controller with default template
and show the products those i have under the "product categorie" category.

How could I change the category-id??

For example if I use this: http://localhost/hika/productlisting i see the main category.

I want to list the subcategories of the category 21 for example:
http://localhost/hika/productlisting?cid=21

(but of course it's not working just a little explanation what I want)

Any advice? What should I do?

Okay.. Sorted.. I just added the ctrl parameter and working fine ))

localhost/hika/productlisting?cid=21&ctrl=category