The Texas Instruments SN74LS42N is a 1-of-10 BCD-to-decimal decoder/demultiplexer from the 74LS Schottky TTL family. It takes a 4-bit BCD input and asserts one of ten active-low outputs, making it the standard part for driving numeric displays, selecting memory banks, or routing control signals in 5V logic systems. The 16-pin DIP package suits through-hole assembly and rework-friendly boards. The 4.75V to 5.25V supply range means this part expects a regulated 5V rail — not a loosely-tolerated bus.
Output drive and loading
Output high current is 400µA, output low sinks 8mA — standard LS TTL drive levels. Each output can drive one or two standard 74LS inputs directly, but fan-out beyond that needs a buffer. If your design routes this decoder to a bus with multiple loads, budget a 74LS244 or similar line driver on the outputs.
Lifecycle and supply reality
For a legacy 74LS BOM line, this is a stable fit.