What this part is and where it fits
The 5402DM: NOR gate, TTL/H/L series, four independent two-input gates.
Lifecycle and compliance
Note that it is RoHS non-compliant — the leads contain lead (Pb) — so it is suited for military, aerospace, or industrial applications that have a RoHS exemption, or for repair and maintenance of existing equipment where lead-free solder is not required.
Sourcing and availability
Because it is an active, RoHS non-compliant TTL gate, it is not a high-volume commodity — expect to request a quote rather than pull from shelf stock.