English: Four inputs are connected to open-collector buffers (such as the SNx407 IC). If a buffer's input is high, the buffer will be in an high-impedance output state. If a buffer's input is low, the buffer will connect to ground. If all inputs are high, the output will be pulled high by the pull-up resistor. But if any input is low, the output will be pulled low by the buffer for that input. This corresponds to AND in active-high logic, or to OR in active-low logic.