Datasheet in PDF format, 72.1 KB, for the PG12864-D graphic LCD module. The part number points to a 128 by 64 pixel matrix, with D marking the particular variant. Such documents describe pinout, recommended operating conditions, contrast voltage, backlight ratings and mechanical size. A technician can use it to confirm signals at the connector, trace the interface to the main controller and assess replacement options. Check that the fitted module is the D version, since siblings in the series differ in layout.
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 @acodis_lcd_datasheets_EDID. Enginerys does not host this file.
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