RC - connection using RCTime produces strange results

[selbstdual]

Dear readers,
I have attached a RC connection to a Microchip's pin.
Pin ---- 0 to 40 kOhms ---- 100 nF ---- GND

1. Make Pin high
2. Let wait for 20 ms
3. Set pin to high-impedance
4. I let wait, till pin Low becomes low - counting while doing so

Depending on R value it is faster/lasts longer to make pin Low.
I make the value of R be constant and do several measurements. The result is visualized for me.

What can I infer from these values ?



W1:
ADCWert = 0 ;I
TRISA.3 = 0
PORTA.3 = 1
Pause 3

;PORTA.3 = 0 ;II
TRISA.3 = 1
WHILE PORTA.3 = 1
ADCWert = ADCWert + 1
WEND

TRISA.3 = 0 ;III
PORTA.3 = 0
Pause 18

W2:
ADCWert = 0
Low PORTA.3 ; Discharge cap to start
Pause 10 ; Discharge for 10ms
RCTIME PORTA.3,0,ADCWert ; Read potentiometer on Pin3

W3:
ADCWert = 0 ;I
TRISA.3 = 0
PORTA.3 = 1
Pause 3

;PORTA.3 = 0 ;II
TRISA.3 = 1
WHILE PORTA.3 = 1
ADCWert = ADCWert + 1
TRISA.3 = 0
PORTA.3 = 0
TRISA.3 = 1
WEND

TRISA.3 = 0 ;III
PORTA.3 = 0
Pause 18
W4:
ADCWert = 0 ;I
TRISA.3 = 0
PORTA.3 = 1
Pause 3

;PORTA.3 = 0 ;II
TRISA.3 = 1
RCTIME PORTA.3,1,ADCWert

TRISA.3 = 0 ;III
PORTA.3 = 0
Pause 18