Updating textbox/grid programmatically question

[Debralous]

I have a simple page in an iframe and I am getting a value from the
parent and passing it to a textbox in my page which I'm handling in
javascript with:

document.getElementById('<%=SLProjectID.ClientID%>').value =
ProjectID;

This works fine, that is the appropriate value is displayed in the
text box. My problem is that I need this value to be used as a
parameter for a gridcontrol. Currently I have to click on the textbox
and hit enter in order for the grid control to be updated. I have
ispostback = true. I'm clearly missing a step; could someone point
out what I need to do in order to update the grid "automatically"?

Thanks!