Re: PIC16F688 Comparator and VREF Connection
Check for example figure 4-1 in datasheet section 4.2.5 - note 1. If a pin is selected by the comparator mode or by ANSEL to be analog, then digital input is turned off. If TRIS is low for that bit, the digital output is enabled even if analog input is enabled.
So if the comparator mode doesn't use a port A pin, and ANSEL doesn't make that pin analog (for ADC), then the pin can be used as digital input.