Microchip PIC18C601 and PIC18C801 datasheet in a 5.62 MB PDF. These are ROMless microcontrollers designed to run from external program memory, so boards using them also carry a separate memory chip that holds the firmware. The document covers pinouts, the external memory bus, timing and electrical characteristics. When diagnosing, trace the address and data bus to the external memory and check its supply, since a faulty or corrupted memory chip, not the controller, is often the cause.
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