rows not displayed when setScrollTop used

I am using AW.Grid.Extended
when click the last button, I need to show the last rows and move the scrollbar to bottom. I have used following code

var testGrid = new AW.Grid.Extended;
testGrid.setVirtualMode(false);

scroll bar code is

var lastButton = new AW.UI.Button;
lastButton.setControlText("Last");
document.write(lastButton);

lastButton.onControlClicked = function(){
var rowpos = parseInt(totPages.getControlText())* 1226;
testGrid.setScrollTop(rowpos);

Here when we click the last button, scrollbar moving to end of the grid but data is not displaying, If I click on the top of the vertical bar - data is showing.

I also tried
testGrid.raiseEvent("onScrollTopChanged");
testGrid.onScrollTopChanged = function(rowpos){testGrid.setScrollTop(rowpos); }
but when I use the onScrollTopChanged, scrollbar came to top position.

Please help me........

How are you calculating the scroll amount? Are you sure this is correct one?