Vss
                            |
                            |
                            |
                            |
                            |
                            |
                    Pullup  |
                 .---|R1_|--o
                 |          |
                 |          |
                 |          |
         __      |          |
      -o|  |o-   |          |
      -o|µC|o-   |        |/
      -o|  |o----o--------|  PNP
      -o|__|o-            |<
                            |
                            |
                            |
                            |
                           .-.
                           | |R2
                           | |
                           '-'
                            |
                            |
                            |
                           ===
                           GND


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