Texas Instruments datasheet for the SN74S139N, a dual 2-line-to-4-line decoder and demultiplexer in the Schottky TTL family, housed in the N plastic DIP package. At 15.3 KB the PDF is probably a concise product sheet. On older logic and memory boards this chip often produces chip-select signals, so its pinout helps you check whether a missing enable comes from the decoder or from the logic driving it. Probe the enable and select inputs first, then the active-low outputs, before you replace the IC.
The button opens the matching file on RM Schematics, or a source page if it is not catalogued there yet. The original attachment is from @datasheet_technar_org. Enginerys does not host this file.
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