Ok,
I directly saving the ADRESL and ADRESH register which is used to store the end results of an analog-to-digital conversion (ADC) to results adval and sending LCD. My problem is, the code is working properly only with 4MHz oscillator, when I define 20MHz occillator, the conversion is very slow, waiting few second, when start conversion.
Whay the conversion is fast for 4Mhz oscillator and very slow for 20MHz oscillator

adval = ADRESL + (ADRESH * 256)

and sending LCD

Lcdout $fe, 1 ' Clear LCD
Lcdout "Value: ", DEC adval ' Display the decimal value