XNOR GATE O = A + B 5V SW_A A SW_B B GND R R GND O A = 0 / L / 0V B = 0 / L / 0V O = 1 / H / 5V LED : ON A B A+B O 0 0 0 1 0 1 1 0 1 0 1 0 1 1 0 1 XNOR Gate IC * 74266 (TTL) * 4077 (CMOS)