Logic function and parametric fit
The SN74HCS138DR is a 3-line to 8-line decoder/demultiplexer from the 74HCS series, containing one independent 1 x 3:8 circuit. It takes a 3-bit binary input and activates one of eight active-low outputs, which is the standard address-decoding function for memory-mapped I/O or chip-select generation in digital systems. Each output can source or sink 7.8 mA, which is sufficient to drive a single TTL load or an LED indicator directly, though a buffer is needed for heavier bus loads.
Temperature grade and package
The supplier device package is 16-SOIC, and the mounting type is surface mount. The narrow-body SOIC footprint is shared across many logic families, so a single PCB layout can accommodate the 74HCS138 alongside older 74HC or 74HCT parts if a design migration is needed.