Full datasheet for the ATmega169 AVR microcontroller, distributed as a 2.97 MB PDF. This part includes an integrated LCD controller, and the document covers its segment and common drivers alongside the usual timers, serial interfaces, ADC, JTAG and electrical data. Technicians use it to trace LCD lines, power and programming pins on equipment that drives a segment display directly from the chip, and to set fuses correctly before reflashing. Check the chip marking and package against the ordering information.
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.