Full datasheet for the tiny28 device, a name that matches the Atmel AVR ATtiny28 8-bit microcontroller family, supplied as a 933 KB PDF. The name gives no revision or package details, so check the document's own revision footer. A datasheet like this covers the pinout, electrical characteristics, memory map, clock options and programming interface. Technicians use it to confirm supply voltage limits, identify pins when probing a suspect controller, and check the marking on the chip against the part described before replacing or reprogramming it.
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.
How to open a .pdf file
The standard format for schematics, block diagrams, power-sequence charts and service manuals.