As per the logic I done in code, the controller output I should get is 0.5. I tested in open loop with multi Meter and got 0.5. But when I connect to load, and getting 0.8V. why this problem comes and how to correct it?
Your circuit, your code and details of the load would assist greatly
What the heck are you talking about.
Is this a cross-post?
Seems to be continuation of this 2 position temperature controller with logic gates - #9 by britto - Programming Questions - Arduino Forum
But he has always refused to post any hardware diagrams so I suggest we either ignore this or wait until he does.
No Grumpy, it is completely different.
britto:
No Grumpy, it is completely different.
If it is;
Please read the first post in any forum entitled how to use this forum.
http://forum.arduino.cc/index.php/topic,148850.0.html
Can you please post a copy of your circuit, in CAD or a picture of a hand drawn circuit in jpg, png?
Please include your power supply and label components and pins.
Thanks.. Tom... 
britto:
No Grumpy, it is completely different.
Then for god’s sake describe your problem so people who are not sat in front of it can understand what it is you are doing.
My crystal ball seems a bit cloudy at present.
Without a complete set of data we can't help.
Allan
britto:
As per the logic I done in code, the controller output I should get is 0.5. I tested in open loop with multi Meter and got 0.5. But when I connect to load, and getting 0.8V. why this problem comes and how to correct it?
If the load is between the output and supply, say 5V, then that can be expected.
What is the load?
Can you please post a copy of your circuit, in CAD or a picture of a hand drawn circuit in jpg, png?
Thanks.. Tom..