CPU

The NES CPU core is based on the 6502 processor and runs at approximately 1.79 MHz (1.66 MHz in a PAL NES). It is made by Ricoh and lacks the MOS6502's decimal mode. In the NTSC NES, the RP2A03 chip contains the CPU and APU; in the PAL NES, the CPU and APU are contained within the RP2A07 chip.

Section

• Memory map
• Pinout
• Powerup state
• status flag behavior

Note

• The CPU's clock is obtained by dividing a 21.477272 MHz clock source by 12 (26.601712 MHz divided by 16 for PAL).
• Kevtris has confirmed that all illegal 6502 opcodes execute identically on the 2A03/2A07. He has even went as far as to integrate them into the CopyNES BIOS.
• For the CPU instruction list, please refer to this section.
• A printer friendly version covering all section is available here.