 Since current cannot flow through LEDs in reverse direction at this low voltage, LED2 will remain unlit.If the voltages on pin X1 and pin X2 are reversed, LED2 will light and LED1 will be unlit.The Charlieplexing technique does not actually make a larger matrix possible when only using two pins, because two LEDs can be driven by two pins without any matrix connections, and without even using tri-state mode.