What this 54S153DM is — a TTL 4-line multiplexer
The 54S153DM is a TTL multiplexer that selects one of four input lines and routes it to a single output.
Lifecycle and compliance — still active, but RoHS-exempt only
However, it is RoHS non-compliant — the lead-bearing finish is typical of legacy military/industrial TTL parts. This part fits BOMs that have a RoHS exemption (e.g., aerospace, defence, high-reliability industrial) or are grandfathered into leaded solder processes. For RoHS-mandated builds, a lead-free equivalent would need to be sourced; no such alternate is listed in the record.