the orientation, the logic changes somewhat. In particular,
the columns which become the common anodes must now
be driven by PNP transistors and the newly christened row
select lines are made active by grounding them. In short,
negative logic is now the name of the game. That’s the sort
of thing microcontrollers are well suited for sorting out.
We’ll still use the PIC circuitry of Figure 3, but simply
exchange the “row” and “column” labels. Note, too, that pin
Figure 7. Drive this horizontal two-digit display with the PIC circuit of Figure 3, swapping the row
and column labels. Now, port A controls the rows and port B controls the columns; pin 12 of the PIC is not needed.
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