You seem to have edited your post. You said you were using a 0.1uF capacitor. Now it's ten times larger!
The time constant (TC) for 1uF * 10K = 0.01 Seconds (10mS). The time it takes to charge (or discharge) a capacitor by 85% is about 2 time constants (2TC). So it will take about 20mS to discharge that capacitor from 5v to <1v. Far too long. You are aiming for 2TC of about 500uS (about 1/40th of your current figure). Also, it will be hard to charge such a large capacitor in 1uS, so your 'weak' port might not be charging the cap enough.
Remember: TC (in Seconds) = C (in Farads) * R (In ohms)
You want a 2TC of around 500uS (0.0005 Seconds) for discharging.
You want a 2TC of about 1uS (0.000001 Seconds) for charging.
Also bear in mind that the discharge resistor is effectively the lower leg of a divider, the upper leg being the output resistance of your port, so don't make it too small.
EG: A 22nF capacitor * 10k resistor has a 2TC of about 440uS and as long as your port has an output impedance of less than 25R, then it will have a charging 2TC of 1uS or less. (2uS for 50R, 4uS for 100R etc).
Measure the output resistance, calculate the required capacitor, then the discharge resistor. Use a signal diode (not a rectifier diode). As far as I know, any capacitor type should be ok, as long as it's on spec.
The time constant (TC) for 1uF * 10K = 0.01 Seconds (10mS). The time it takes to charge (or discharge) a capacitor by 85% is about 2 time constants (2TC). So it will take about 20mS to discharge that capacitor from 5v to <1v. Far too long. You are aiming for 2TC of about 500uS (about 1/40th of your current figure). Also, it will be hard to charge such a large capacitor in 1uS, so your 'weak' port might not be charging the cap enough.
Remember: TC (in Seconds) = C (in Farads) * R (In ohms)
You want a 2TC of around 500uS (0.0005 Seconds) for discharging.
You want a 2TC of about 1uS (0.000001 Seconds) for charging.
Also bear in mind that the discharge resistor is effectively the lower leg of a divider, the upper leg being the output resistance of your port, so don't make it too small.
EG: A 22nF capacitor * 10k resistor has a 2TC of about 440uS and as long as your port has an output impedance of less than 25R, then it will have a charging 2TC of 1uS or less. (2uS for 50R, 4uS for 100R etc).
Measure the output resistance, calculate the required capacitor, then the discharge resistor. Use a signal diode (not a rectifier diode). As far as I know, any capacitor type should be ok, as long as it's on spec.