NES Programming

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The NES (Nintendo Entertainment System) is an 8-bit console popular in the 1980s and 1990s.

Contents 1 Hardware specifications 2 6502 CPU memory map 3 Tutorials 4 Appendices 5 Hardware I/O ports 5.1 PPU 5.2 Video control 5.3 PPU (continued) 5.4 Sound 5.5 DMC 5.6 Sprites (continued) 5.7 Sound (continued) 5.8 Joystick 6 External links

[edit] Hardware specifications

• CPU - Ricoh 2A03 CPU which is a MOS 6502 without a decimal mode.
  • Clocked 1.789773Mhz for NTSC (System 21.47727Mhz / 12) and 1.773447Mhz for PAL (System 26.601171Mhz / 15)
• Memory - 2 KB
• Video
  • Ricoh 2C02 PPU (Picture Processing Unit)
  • Resolution - 256 x 240 pixels (Only 256 x 224 pixels is visible on NTSC)
  • Colors - Fixed 52 (44 colors, 5 grays and 3 duplicated)
  • Palette
    • Background: 4 Palettes x 3 Colors + 1 Back Color
    • Sprites: 4 Palettes x 3 Colors
  • Tiles - 8 x 8 pixels tiled background
  • Sprites - Up to 64 8x8-pixel or 8x16 pixel sprites but only 8 can be displayed per scan-line
• Sound
  • 2 Pulse wave channels
  • 1 Triangle wave channel
  • 1 Noise channel
  • 1 DPCM channel

[edit] 6502 CPU memory map

Address Range (Hexadecimal)	Size	Notes (Page size is 256 bytes)
$0000 - $00FF	256 bytes	Zero Page - Special Zero Page addressing modes give faster memory read/write access
$0100 - $01FF	256 bytes	Stack memory
$0200 - $07FF	1536 bytes	RAM
$0800 - $0FFF	2048 bytes	Mirror of $0000-$07FF	$0800-$08FF Zero Page $0900-$09FF Stack $0A00-$0FFF RAM
$1000 - $17FF	2048 bytes	Mirror of $0000-$07FF	$1000-$10FF Zero Page $1100-$11FF Stack $1200-$17FF RAM
$1800 - $1FFF	2048 bytes	Mirror of $0000-$07FF	$1800-$18FF Zero Page $1900-$19FF Stack $1A00-$1FFF RAM
$2000 - $2007	8 bytes	Input/Output registers
$2008 - $3FFF	8184 bytes	Mirror of $2000-$2007 (multiple times)
$4000 - $401F	32 bytes	Input/Output registers
$4020 - $5FFF	8160 bytes	Expansion ROM - Used with Nintendo's MMC5 to expand the capabilities of VRAM.
$6000 - $7FFF	8192 bytes	SRAM - Save Ram used to save data between game plays.
$8000 - $BFFF	16384 bytes	PRG-ROM lower bank - executable code
$C000 - $FFFF	16384 bytes	PRG-ROM upper bank - executable code
$FFFA - $FFFB	2 bytes	Address of Non Maskable Interrupt (NMI) handler routine
$FFFC - $FFFD	2 bytes	Address of Power on reset handler routine
$FFFE - $FFFF	2 bytes	Address of Break (BRK instruction) handler routine

[edit] Tutorials

• A few words on assembly
• Initializing the NES
• Adding Graphics
• Adding Sound

[edit] Appendices

• The NES memory map
• NES hardware registers
• NES Graphics

[edit] Hardware I/O ports

The NES has I/O ports located at addresses $2000-$2007 (hexadecimal) and $4000-$4017.

[edit] PPU

• $2000 - write only - PPU Control Register 1
• $2001 - write only - PPU Control Register 2
• $2002 - read only - PPU Status Register

[edit] Video control

• Sprites
  • $2003 - write only - Sprite Memory Address
  • $2004 - read / write - Sprite Memory Data
  • $2005 - write only - Background Scroll

[edit] PPU (continued)

• $2006 - write only - PPU Memory Address - indexing into PPU memory location
• $2007 - read / write - PPU Memory Data - data to read from a PPU memory location or write to a PPU memory location

[edit] Sound

• Square wave 1
  • $4000 - Register 1 - Bits:
    • 0-3: volume / envelope decay rate
    • 4: envelope decay disable
    • 5: length counter clock disable / envelope decay looping enable
    • 6-7: duty cycle type (unused on noise channel)
  • $4001 - Register 2 - Bits:
    • 0-2: right shift amount
    • 3: decrease / increase (1/0) wavelength
    • 4-6: sweep update rate
    • 7: sweep enable
  • $4002 - Register 3 - Bits:
    • 0-7 Eight LSB of wavelength
  • $4003 - Register 4 - Bits:
    • 0-2: 3 MS bits of wavelength (unused on noise channel)
    • 3-7: length counter load register
• Square wave 2
  • $4004 - Register 1 - Same as Square wave 1
  • $4005 - Register 2 - Same as Square wave 1
  • $4006 - Register 3 - Same as Square wave 1
  • $4007 - Register 4 - Same as Square wave 1
• Triangle
  • $4008 - Register 1 - Bits:
    • 0-6 linear counter load register
    • 7 length counter clock disable / linear counter start
  • $4009 - Unused Register
  • $400A - Register 3 - Same as Square wave 1
  • $400B - Register 4 - Same as Square wave 1
• Noise
  • $400C - Register 1 - Same as Square wave 1
  • $400D - Unused Register
  • $400E - Register 3 - Bits:
    • 0-3 playback sample rate
    • 4-6 unused
    • 7 random number type generation
  • $400F - Register 4 - Same as Square wave 1

[edit] DMC

• $4010 - ???? - ????
• $4011 - ???? - ????
• $4012 - ???? - ????
• $4013 - ???? - ????

[edit] Sprites (continued)

• $4014 - write only - DMA Access to the Sprite Memory

[edit] Sound (continued)

• • $4015 - read / write - enable/disable individual sound channels

[edit] Joystick

• • $4016 - read / write - Joystick 1
  • $4017 - read / write - Joystick 2

[edit] External links

• More info can be found on IRC, on the EFnet server, in channel #nesdev
• NesDev, contains detailed technical documents, tools, and examples.
• P65 Assembler, an assembler written in Perl for the 6502 family of processors with support for programming the NES.