The IN74ACT251 is identical in pinout to the LS/ALS251, HC/HCT251. The IN74ACT251 may be used as a level converter for interfacing TTL or NMOS outputs to High Speed CMOS inputs.
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 IN74ACT251 to be used in bus-oriented systems.

• TTL/NMOS Compatible Input Levels
• Outputs Directly Interface to CMOS, NMOS, and TTL
• Operating Voltage Range: 4.5 to 5.5 V
• Low Input Current: 1.0 µA; 0.1 µA @ 25°C
• Outputs Source/Sink 24 mA