Thus, another problem is PWM command...

let say,
MsCommOutput="127"

PIC Side:
SERIN2 SerPin,BAUD,[DEC YourVar]
if YouVar=127 then goto GetABeer

I put YouVar into pwm, portc.1,YouVar,100
my DC motor will run at half speed at the short period (0.05mili secs), then motor will run at full speed after that.

So, what is the problem? I feel very happy to know the reason...anyway, thanks u