I'm having trouble with an I/O function.

I have a capacitor, connected through three resistors, to three I/O pins.
The Capsense pin connects to the cap through a 1k resistor.
The other two pins are varying resistance.
If I set them as inputs, then the resistances don't matter.
If I set either one as output, then it charges or discharges the cap at a
rate determined by it's resistor.

The basic idea is to read the cap RC time constant, as a form of A/D converter.

Everything's fine, till I get to the point where I want to watch the cap
discharge, until it's low, before taking one of the other pins to output high.

Read_Function:
        btfsc   PORTB,Capsense          ;loop here till low on cap sense pin
        goto    Read_Function           ;

The Capsense pin is set as an input, as is one of the other two pins
The third is an output, and I can see that it is low, and that the voltage
on the capsense pin is also low, but the code loops here forever,
indicating that it's seeing a high input.

I've walked through all the banking, and I believe that I'm in the right
banks when I'm talking to PORTB and TRISB.

I've disabled all peripherals that would otherwise use portb pins.

So, how could I get stuck here, given a low on the Capsense pin of portb?

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