Datasheet for the Microchip PIC16C72, an 8-bit OTP or EPROM microcontroller with an analog-to-digital converter, supplied as a 1.13 MB PDF. It is a 28-pin device, and the document covers its pin functions, memory organisation, timers, serial port and electrical characteristics. Technicians use it to trace signals and confirm power, clock and reset on a control board. Being non-flash, a defective chip must be replaced with a part programmed with the original firmware, which is not included here.
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.