refresh child iframe with integration of asp.net and javascript

hi to all,
i have a problem with asp.net c# and iframes.... I've noticed that the integration of these

two components is very low...

My scenario is the follow:
in my parent page, i have a button within an updatepanel setted with updatemode=always...

when i click this button, it open a modalpopupextender that contain my iframe...

I would like to refresh\reload my iframe after the ModalPopUp.show(), beacuse in that moment

at the form_load, dynamic controls will create....

how can i do this?
Surfing the internet,i read that I must use the integration with javascript from my Parent

page to reload the iframe...

Thanks in advance