The IN74ACT643 is identical in pinout to the LS/ALS643, HC/HCT643. The IN74ACT623 may be used as a level converter for interfacing TTL or NMOS outputs to High Speed CMOS inputs.
The IN74ACT643 is a 3-state transceiver that is used for 2-way asynchronous communication between data buses. The device has an active-low Output Enable pin, which is used to place the I/O ports into high-impedance states. The Direction control determines whether data flows from A to B or from B to A.

• 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