[in progress]
So that all works out nicely in theory. There is one last small hurdle
to jump before we can implement it in our hardware, however. According
to the PIC documentation, each IO pin can sink or source up to 25 mA.
That's not very much! Enough to light an LED (with a resistor!), but
not nearly enough to power an entire 7-segment digit (which may consume
closer to 70 mA, for example). This means that while we can power the
individual segments (lines a-g) with the IO pin directly, we need to
buffer lines 1-3).
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