What this part is — AND-OR-INVERT gate
The 54S64DM is a single AND-OR-INVERT gate from the 54S Schottky TTL logic family. It implements the logic function (A·B) + (C·D) inverted at the output — a compact two-wide, two-input AND-OR-INVERT structure. This is a through-hole part supplied in Bulk tube or tray, typical for legacy or high-reliability board builds that still use 54S-series logic.
What the logic function means for your design
An AND-OR-INVERT gate collapses two AND terms into a single NOR output. In a typical glue-logic role, it replaces two AND gates plus a NOR gate, saving one package. The 54S series uses Schottky clamping to reduce propagation delay, so this gate is faster than standard 54LS parts — useful in timing-critical paths where you need the AND-OR-INVERT function without adding a full PLD.