The ’AHCT125 devices are quadruple bus buffer gates featuring independent line drivers with 3-state outputs. Each output is disabled when the associated output-enable (OE)\ input is high. When OE\ is low, the respective gate passes the data from the A input to its Y output.
To ensure the high-impedance state during power up or power down, OE\ should be tied to VCC through a pullup resistor; the minimum value of the resistor is determined by the current-sinking capability of the driver.
"Level shifting chips let you connect 3V and 5V devices together safely. This chip is particularly good at converting 3V logic up to 5V. This is in demand especially when connecting some 3V devices such as the Teensy 3 to NeoPixels! Just power the 74AHCT125 with 5V, it will detect 3V logic properly. You can also use it to connect 5V logic out to 3V logic in, thats when you want to power the 74AHCT125 with 3V, it can safely read 5V logic on the input pins."