hi!
Actually, mahmood Elnasser it was my mistake, When i read your reply i didnot understand it in the way Rustu Kaya said. What i understand was that use a DAC's output to control VCO's input. In this sense i have to use DAC (or MCU with DAC) and also the output will depands upon entirly on DAC and VCO accuracy (or tolarence) and also for accuracy i have to feedback output to MCU to sense its frequency. Then you mention using PLL to generate frequency which i think was to only use its VCO. So i did not get the point which Rustu Kaya said later and thought it was the first time that point is said. I think many other people will also not get the point in your post which Rustu Kaya said because you did not clearly said any thing about putting VCOs sine wave back to PLL to regulate its frequency.
But its not a big deal who gave me the right idea the important thing is that i found a good way to solve my porblem and for this i thank all who participated in this post specially mahmood Elnasser and Rustu Kaya.
Also for Richard Slaughter if you think this discussion is heavy for you then you should study something like diploma in analog electronics ;-)