Device identity and function
The Texas Instruments 54S258FM is a 2-line-input multiplexer with TTL-compatible outputs, classified under the Microcontrollers & Processors category but functionally a logic-level signal selector. It routes one of two digital input lines to a single output under the control of a select line, a standard building block in data-routing and bus-switching applications.
This part is RoHS non-compliant, a legacy lead-bearing finish typical of older TTL logic families. Buyers with RoHS-exempt or military/industrial BOM positions should confirm the solder process compatibility before committing.