This Side of Sanity
alternate history: eight bit computer

alternate history: eight bit computer

The real world timeline is shown side by side with this alternate history (and marked with a gray background).

MOS Technology 6502

Chuck Peddle led a small team at MOS Technology to create the 6502 in 1975

memory map and registers

A - Accumulator - 8 bits

Y - Index Register Y - 8 bits

X - Index Register X - 8 bits

PCH & PCL - Program Counter - 16 bits

00000001 S - Stack Pointer - 16 bits

data bus buffer -- second and third bytes of instruction, if used, routed to either ALU or PC

PCR - Processor Status register - 8 bits

    N V I B D I Z C

        N = Negative (1 = negative)

        V = Overflow (1 = true)

        I

        B = Break Command (1 = break)

        D = Decimal Mode (1 = true)

        I = IRQ Disable (1 = disable)

        Z = Zero (1 = true)

        C = Carry (1 = true)