about take a feedback and error detection in set speed and feeback

i was write the script to detect the the error in set speed by analog input pot.1 and read a feedback and it will be compare it but is it not working what can i do now.....
my script is.....for vbl2360

in closed loop position tracking mode

dim set_speed as integer
dim Fedback as integer

top:


set_speed = getvalue(_AIC,2)

Fedback = getvalue(_F,2)

if (set_speed = Fedback) then

setcommand(_GO, 2, 0)

elseif(set_speed > Fedback)

setcommand(_GO, 2, -(set_speed - Fedback))

elseif(set_speed < Fedback)

setcommand(_GO, 2, (Fedback - set_speed ))
else

end if


goto top

i want to send command from hyper terminal with given setting in user manual and i send this

!P 2 50
but it is nothing happen and i got same reply from controller

actually i don't know how should go to 50 rotation of motor and stop there until next position command