PDF datasheet for the SN74S1055SD, a part carrying the 74S designation used for Schottky TTL logic; the name does not spell out its function, so the document should be read to confirm it. At about 20 KB it is a brief sheet, likely holding pinout and key ratings. Technicians use such references to identify pins, supply connections and logic levels when diagnosing boards built around TTL glue logic. Check that the full marking and package suffix on the chip match the document before relying on it.
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