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
• Power up state
• status flag behavior

Note

The CPU generates its clock signal by dividing the master clock signal.

Rate	NTSC NES/Famicom	PAL NES	PAL Famiclone
Color subcarrier frequency fs (exact)	39375000/11 Hz	4433618.75 Hz	4433618.75 Hz
Color subcarrier frequency fs (approx)	3.579545 MHz	4.433619 MHz	4.433619 MHz
Master clock frequency 6fs	21.477272 MHz	26.601712 MHz	26.601712 MHz
Clock divisor d	12	16	15
CPU clock frequency 6fs/d	1.789773 MHz	1.662607 MHz	1.773448 MHz

• 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.
• The CPU pinout is located in the hardware pinout section here
• For the CPU instruction list, please refer to this section.

• A printer friendly version covering all section is available here.