MOS Technology 6502 microprocessor family

MOS Technology 6502 and other 650x/651x processors are a family of inexpensive 8-bit microprocessors. 6502 and 6512 processors could address 64KB of memory, other CPUs in the family could address up to 8 KB. Stack size of the 6502 was limited to 256 bytes. The processors had only 6 registers, and only one of these registers - an accumulator - could be used for arithmetic and logic operations. The 6502 microprocessor had 13 addressing modes, some of these modes made extensive use of two 8-bit index registers. The processor didn't have I/O instructions, therefore 6502-based computers used memory mapped I/O.

All microprocessors in the NMOS 6502/650x family are software compatible between each other - the differences between CPUs are in hardware (different maximum size of addressed memory, clock oscillator is on-board or external, interrupt input options). CMOS 65Cxx and 65SCxx microprocessors add new instructions and addressing modes, and new hardware features such as memory lock and bus enable signals. For more information please see list of differences between 65xx, 65Cxx and 65SCxx CPUs.