then why this doesnt work:

I have a potentiometer on pin 0 (AD), and when I turn that pot to one end (left or right) my values of variable should be 0 or 255. And when I wrote IF function nothing happens

for example:

start:
ADCIN 0, pw
if pw = 0 then
Pulsout portd.2, 220
else
goto start
endif
goto start

when ever I wrote pw = 255 or pw = 0 it doesnt do anything, but when I wrote If pw > 220 then it works ????