The SN74AC240 device is organized as two 4-bit buffers/drivers with separate output-enable (OE) inputs. When OE is low, the device passes inverted data from the A inputs to the Y outputs. When OE is high, the outputs are in the high-impedance state.

To ensure the high-impedance state during power up or power down, OE should be tied to V_CC through a pullup resistor; the minimum value of the resistor is determined by the current-sinking capability of the driver.