Datasheet for the Microchip dsPIC30F family of digital signal controllers, supplied as a 5.10 MB PDF. The name identifies only the family, so check inside which specific devices and revision the document covers. Technicians use such a reference to look up pinouts, supply and oscillator pins, programming pins for ICSP, and peripheral registers when diagnosing or reprogramming a board built around one of these chips. Compare the full part marking on the package with the device tables before relying on any pin assignment.
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. Enginerys does not host this file.
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The standard format for schematics, block diagrams, power-sequence charts and service manuals.