Input pin impedance?

[pneumatic]

How high is the impedance on a uC input pin? Or put another way, how large a pullup resistor can I use? I know the convention is to use 10K, but what if I use 47K? will it still work?

-- Mitch (who has a bunch of 47K resistors laying around.. and wants to reduce drain on a bunch of inputs)

[adafruit]

you can check the datasheet but it is much more than 100K, probably 1M?

[eil]

Not an expert, but I would imagine 47k would work fine in most cases.

[westfw]

For CMOS digital input pins, the input impedance if very high indeed, and level of noise and other signals present in the circuit is probably more important to take into consideration for pullups than the pin itself.
47k is probably OK in general, but you're approaching the range that you could change the pin state with your finger, if you are otherwise grounded...