The 6502

The 6502 microprocessor


Brief history of the 6502
The 6502 is an 8-bit microprocessor that was introduced in 1975 as a low cost alternative to the market at that time still beeing a fully functional CPU with all the basic funcionalities one requires in a CPU. It became popular among hobbyist and was used in many of the most popular early stage microcomputers such as Apple I & II, Commodore 64, PET & VIC-20, Atari 2600, BBC Micro and arcade cabinets.

Technical description
  • 8-bit microprocessor
  • 16-bit address bus (64KB address space)
  • 1-2 MHz external clock
  • Registers
    • Accumulator (A) (8-bit)
    • Two index registers (X & Y) (8-bit)
    • Stack pointer (S) (8-bit)
    • Program counter (PC) (16-bit)
  • Several addressing modes (implied; absolute; indexed; indexed zero-page; relative; accumulator; indirect x & y; immediate)
  • Interrupts (two lines)
    • NMI (non-maskable interrupt line)
    • IRG (maskable interrupt line)
  • 151 documented opcodes
  • Little endian addressing