The IN74AC251 is identical in pinout to the LS/ALS251, HC/HCT251. The device inputs are compatible with standard CMOS outputs; with pullup resistors, they are compatible with LS/ALS outputs.
The device selects one of the eight binary Data Inputs, as determined by the Address Inputs. The Output Enable pin must be at a low level for the selected data to appear at the outputs. If Output Enable is high, the Y and the Y outputs are in the high-impedance state. This 3-State feature allows the IN74AC251 to be used in bus-oriented systems.

• Outputs Directly Interface to CMOS, NMOS, and TTL
• Operating Voltage Range: 2.0 to 6.0 V
• Low Input Current: 1.0 µA; 0.1 µA @ 25°C
• High Noise Immunity Characteristic of CMOS Devices
• Outputs Source/Sink 24 mA