The IN74HC138A is identical in pinout to the LS/ALS138. The device inputs are compatible with standard CMOS outputs; with pullup resistors, they are compatible with LS/ALSTTL outputs.
The IN74HC138A decodes a three-bit Address to one-of-eight active-low outputs. This device features three Chip Select inputs, two active-low and one active-high to facilitate the demultiplexing, cascading, and chip-selecting functions. The demultiplexing function is accomplished by using the Address inputs to select the desired device output; one of the Chip Selects is used as a data input while the other Chip Selects are held in their active states.

• Outputs Directly Interface to CMOS, NMOS, and TTL
• Operating Voltage Range: 2.0 to 6.0 V
• Low Input Current: 1.0 µA
• High Noise Immunity Characteristic of CMOS Devices