The SN74S138AN is a high-speed 3-line to 8-line decoder / demultiplexer IC from the 74S TTL logic family. It takes a 3-bit binary input (A, B, C) and decodes it into 8 mutually exclusive active outputs (Y0–Y7).

Only one output line is activated at a time based on the binary input combination, making it ideal for address decoding, memory selection, and control signal routing in digital systems.

Key features include:

3-to-8 line decoder / demultiplexer
TTL 74S (Schottky) high-speed logic family
3 input lines → 8 output lines (1-of-8 selection)
Active-low outputs (only one output goes LOW at a time)
Enable inputs for system control (G1, G2A, G2B)
Very fast propagation delay compared to standard 74LS series
16-pin DIP package (SN74S138AN)
Designed for 5V TTL logic systems
Used in memory decoding, chip select logic, and multiplexing control