Quad 2:1 multiplexer on a 5V bus
The Texas Instruments SN74LS158DR is a 74LS-series quad 2:1 multiplexer — four independent 2-input muxes sharing a common select and output-enable line. It routes one of two 4-bit data sources onto a single output bus, a common pattern in address decoding, data-path steering, and register-file readback for 5V logic systems. The 16-SOIC package fits surface-mount assemblies where through-hole 74LS parts are being retired.
Output drive and fan-out
High-level output current is 400 µA, low-level sinks 8 mA. That 8 mA sink is enough to drive one or two standard LS TTL loads but not a relay coil, LED indicator, or a long backplane trace without a buffer. Plan a line driver or pull-up resistor if the output must drive more than a few milliamperes.