Analog pin to ground? GPIO low voltage not 0? I/O impedance?

[antoine]

I have a few questions (using nRF51 DK and/or external nRF51822)

1. I use an analog pin to measure the voltage of a capacitor of an analog circuit. From time to time, I would like to discharge the capacitor by setting the analog pin to the ground programmatically. Is this possible?

2. What is the input impedance of an analog pin when using ADC?

3. I want to use a GPIO pin to control the input voltage of an analog circuit to high or low level. With a voltmeter (on the pin 0.22, also connected to LED2), I get 2.9V and 0.21V readings when I toggle LED2. I need the low level to be exactly 0V (ground)? Is it possible?

4. Whether set to high or low, what are the output impedance of a non-analog pin used as output?

5. Can an analog pin be used as an analog output (I guess not but I would like to confirm)?

Regards

[RK]

1. yes - disconnect from ADC, set low, reconnect again

2. complicated - it's in the reference manual

3. 2.9V and .21V are within spec for high and low, I would have expected the 0.21V to be closer to ground, normally is when I measure it, but you can't guarantee it beyond what's spec'ed

4. don't know try the manual for that too

5. No - there is no analog out.

[antoine]

Thank you.

I could not find information about the low voltage on the reference manual.

Actually, it doesn't really matter if it is exactly 0V for my application, as long as 2 conditions are fulfilled: a) Is the low voltage exactly the same on all pins set to low? b) Is it constant over time?

Would you know about that?