This is my working code :
calibration:
rel1=1 ' rel1 = 1 -->> window roll-up !
for cnt=1 to 80 ' assuming window roll-up complete in 8 seconds !
adcin 3, v_cal
v_cal=v_cal * 5000
v_cal=div32 1023
vmax=0 max v_cal
pause 100
next cnt

low rel1
calibra = vmax
if calibra > 20 then ' "20" is value knowing by user !
write 0, calibra.byte1
pause 10
write 1, calibra.byte0
pause 10
else
calibra = 19
write 0, calibra.byte1
pause 10
write 1, calibra.byte0
pause 10
endif
RETURN