CPU memory map

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Address range Size Device
$0000–$07FF $0800 2 KB internal RAM
$0800–$0FFF $0800 Mirrors of $0000–$07FF
$1000–$17FF $0800
$1800–$1FFF $0800
$2000–$2007 $0008 NES PPU registers
$2008–$3FFF $1FF8 Mirrors of $2000–$2007 (repeats every 8 bytes)
$4000–$4017 $0018 NES APU and I/O registers
$4018–$401F $0008 APU and I/O functionality that is normally disabled. See CPU Test Mode.
$4020–$FFFF $BFE0 Cartridge space: PRG ROM, PRG RAM, and mapper registers (see note)

Some parts of the 2 KiB of internal RAM at $0000–$07FF have predefined purposes dictated by the 6502 architecture. The zero page is $0000–$00FF, and the stack always uses some part of the $0100–$01FF page. Games may divide up the rest however the programmer deems useful. See Sample RAM map for an example allocation strategy for this RAM.

Note: Most common boards and iNES mappers address ROM and Save/Work RAM in this format:

  • $6000–$7FFF = Battery Backed Save or Work RAM
  • $8000–$FFFF = Usual ROM, commonly with Mapper Registers (see MMC1 and UxROM for example)

If using DMC audio:

  • $C000–$FFF1 = DPCM samples

The CPU expects interrupt vectors in a fixed place at the end of the cartridge space:

  • $FFFA–$FFFB = NMI vector
  • $FFFC–$FFFD = Reset vector
  • $FFFE–$FFFF = IRQ/BRK vector

If a mapper doesn't fix $FFFA–$FFFF to some known bank (typically, along with the rest of the bank containing them, e.g. $C000–$FFFF for a 16KiB banking mapper) or use some sort of reset detection, the vectors need to be stored in all banks.