i have a main page when i click the link i want to change the src of child
frames of window.. when i use  window.parent.sa.src it doesnt work

i can also add an image with id .. how can i manage this image..
parent.sa.imageid.src like this help me please?

//////////////////////////////////////////////

<iframe id="sa" name="sa" src="y.htm" height="100" width="500"></iframe>
<br><br>
<iframe src="x.htm" height="500" width="300" name="yy" id="yy"></iframe>

//////////////////////////////////////////////

x.htm
***************************
<script>
function git()
{window.parent.sa.src='http://www.yahoo.com'}
</script>
<a href="javascript:git()">TIKLA </a>
************************

y.htm

-----------------------------------------------
<script>
function git()
{parent.yy.location.reload('http://www.google.com')}
</script>
<a href="javascript:git()">TIKLA </a>
---------------------------------------------