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Microchip PIC16F84A

The PIC16F84A is Microchip's iconic 8-bit hobbyist microcontroller — the mid-range PIC a whole generation learned assembly on. It is a Harvard machine with 14-bit program words in a 1K flash, a separate 8-bit data memory (the special-function registers plus 68 bytes of general-purpose RAM), an 8-bit working register W, a 13-bit program counter and an 8-level hardware call stack. The full 35-instruction mid-range set, TMR0 with its prescaler, PORTA/PORTB with TRIS latches, a single interrupt vector at 0x0004 and 64 bytes of data EEPROM round it out. Here the whole chip is modelled from scratch in JavaScript, running real assembled firmware.