Today I setup a 12F683 hoping to read pins 2,3, and 4 masked out as a 3-bit word.
I set the chip's bit config to turn off MCLR on pin 4 gpio.3

Pin 4 when not used as a MCLR reset functions as input only.
So I set pins 2, and 3 also as inputs

Then I put 10K resistors on each - pulling them down to ground.
I then set the code to read GPIO and mask out all the other pins.
Then right-shifted the results to derive the lowest 3 bits

Pulling any combination of these 3 pins high should result in values ranging 0-7.

Pins 2, and 3 acted as expected.
However, the MCLR pin was acting flaky.
Even with the pull down resistor on it - it was flipping back and forth between a high and low reading.
I've never seen this before.

I dug through the datasheet to see if I could find something peculiar about pin-4 MCLR with no success.