Window scroll issue for continuous data

Hi ,
in mdi window, I am appending data continuously , i want to make scroll bar independent of data, if i stopped appending data to mdi window then this scroll will work properly, otherwise if data is continuously appending , even if we scroll to top, scroll will come to bottom, i tried scroll at bottom and top, but i don't want top or bottom, it should independent. for example Qt creator compile output window scrollbar, give some suggestions to solve this issue.