PPU memory map: Difference between revisions

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=== PPU VRAM memory map ===
=== PPU memory map ===
 
The [[PPU]] addresses a 14-bit (16kB) address space, $0000-$3FFF, completely separate from the CPU's address bus. It is either directly accessed by the PPU itself, or via the CPU with [[PPU registers|memory mapped registers]] at $2006 and $2007.


{| class="tabular"
{| class="tabular"
! Address range || Size || Description
! Address range || Size || Description || Mapped by
|-
|-
| $0000-$0FFF || $1000 || [[PPU pattern tables|Pattern Table]] 0 [lower CHR bank]
| $0000-$0FFF || $1000 || [[PPU pattern tables|Pattern table]] 0 || Cartridge
|-
|-
| $1000-$1FFF || $1000 || Pattern Table 1 [upper CHR bank]
| $1000-$1FFF || $1000 || Pattern table 1 || Cartridge
|-
|-
| $2000-$23FF || $0400 || [[PPU nametables|Name Table]] #0
| $2000-$23BF || $0400 || [[PPU nametables|Nametable]] 0 || Cartridge
|-
|-
| $2400-$27FF  || $0400 || Name Table #1
| $2400-$27FF  || $0400 || Nametable 1 || Cartridge
|-
|-
| $2800-$2BFF  || $0400 || Name Table #2
| $2800-$2BFF  || $0400 || Nametable 2 || Cartridge
|-
|-
| $2C00-$2FFF  || $0400 || Name Table #3
| $2C00-$2FFF  || $0400 || Nametable 3 || Cartridge
|-
|-
| $3000-$3EFF  || $0F00 || Mirrors of $2000-$2EFF
| $3000-$3EFF  || $0F00 || Unused || Cartridge
|-
|-
| $3F00-$3F1F  || $0020 || [[PPU palettes|Palette RAM]] indexes [not RGB values]
| $3F00-$3F1F  || $0020 || [[PPU palettes|Palette RAM]] indexes || Internal to PPU
|-
|-
| $3F20-$3FFF  || $0080 || Mirrors of $3F00-$3F1F
| $3F20-$3FFF  || $00E0 || Mirrors of $3F00-$3F1F || Internal to PPU
|}
|}


=== Memory details ===
== Hardware mapping ==
 
The NES has 2kB of RAM dedicated to the PPU, usually mapped to the nametable address space from $2000-$2FFF, but this can be rerouted through custom cartridge wiring. The mappings above are the addresses from which the PPU uses to fetch data during rendering. The actual devices that the PPU fetches pattern, name table and attribute table data from is configured by the cartridge.
 
* $0000-1FFF is normally mapped by the cartridge to a [[CHR ROM vs. CHR RAM|CHR-ROM or CHR-RAM]], often with a bank switching mechanism.
 
* $2000-2FFF is normally mapped to the 2kB NES internal VRAM, providing 2 nametables with a [[Mirroring#Nametable_Mirroring|mirroring]] configuration controlled by the cartridge, but it can be partly or fully remapped to ROM or RAM on the cartridge, allowing up to 4 simultaneous nametables.
 
* $3000-3EFF is usually a mirror of the 2kB region from $2000-2EFF. The PPU does not render from this address range, so this space has negligible utility.
 
* $3F00-3FFF is not configurable, always mapped to the internal palette control.
 
== OAM ==
In addition, the PPU internally contains 256 bytes of memory known as [[PPU OAM|Object Attribute Memory]] which determines how sprites are rendered. The CPU can manipulate this memory through [[PPU registers|memory mapped registers]] at [[OAMADDR]] ($2003), [[OAMDATA]] ($2004), and [[OAMDMA]] ($4014). OAM can be viewed as an array with 64 entries. Each entry has 4 bytes: the sprite Y coordinate, the sprite tile number, the sprite attribute, and the sprite X coordinate.
 
{| class="tabular"
{| class="tabular"
! Address || Size || Note || Description
! Address Low Nibble || Description
|-
|-
| $0000 || $1000 || C || Pattern Table #0
| $0, $4, $8, $C || Sprite Y coordinate
|-
|-
| $1000 || $1000 || C || Pattern Table #1
| $1, $5, $9, $D || Sprite tile #
|-
|-
| $2000  ||$03C0 ||  || Name Table #0
| $2, $6, $A, $E || Sprite attribute
|-
|-
| $23C0  ||$0040 || || Attribute Table #0
| $3, $7, $B, $F || Sprite X coordinate
|-
| $2400  ||$03C0 || N || Name Table #1
|-
| $27C0  ||$0040 || N || Attribute Table #1
|-
| $2800  ||$03C0 || N || Name Table #2
|-
| $2BC0  ||$0040 || N || Attribute Table #2
|-
| $2C00  ||$03C0 || N || Name Table #3
|-
| $2FC0  ||$0040 || N || Attribute Table #3
|-
| $3000  ||$0F00 || R ||
|-
| $3F00  ||$0010 ||  || Background palette
|-
| $3F10  ||$0010 ||  || Sprite palette
|-
| $3F20  ||$00E0 || P ||
|}
|}
* C = This memory is not in the NES but on the cartridge board. It can be CHR ROM or CHR RAM.
* N = Mirrored nametables, in a manner controlled by the cartridge board (see [[Mirroring]])
* P = Palette mirror
* R = Mirror of $2000-2EFF (N)

Latest revision as of 22:43, 2 March 2024

PPU memory map

The PPU addresses a 14-bit (16kB) address space, $0000-$3FFF, completely separate from the CPU's address bus. It is either directly accessed by the PPU itself, or via the CPU with memory mapped registers at $2006 and $2007.

Address range Size Description Mapped by
$0000-$0FFF $1000 Pattern table 0 Cartridge
$1000-$1FFF $1000 Pattern table 1 Cartridge
$2000-$23BF $0400 Nametable 0 Cartridge
$2400-$27FF $0400 Nametable 1 Cartridge
$2800-$2BFF $0400 Nametable 2 Cartridge
$2C00-$2FFF $0400 Nametable 3 Cartridge
$3000-$3EFF $0F00 Unused Cartridge
$3F00-$3F1F $0020 Palette RAM indexes Internal to PPU
$3F20-$3FFF $00E0 Mirrors of $3F00-$3F1F Internal to PPU

Hardware mapping

The NES has 2kB of RAM dedicated to the PPU, usually mapped to the nametable address space from $2000-$2FFF, but this can be rerouted through custom cartridge wiring. The mappings above are the addresses from which the PPU uses to fetch data during rendering. The actual devices that the PPU fetches pattern, name table and attribute table data from is configured by the cartridge.

  • $0000-1FFF is normally mapped by the cartridge to a CHR-ROM or CHR-RAM, often with a bank switching mechanism.
  • $2000-2FFF is normally mapped to the 2kB NES internal VRAM, providing 2 nametables with a mirroring configuration controlled by the cartridge, but it can be partly or fully remapped to ROM or RAM on the cartridge, allowing up to 4 simultaneous nametables.
  • $3000-3EFF is usually a mirror of the 2kB region from $2000-2EFF. The PPU does not render from this address range, so this space has negligible utility.
  • $3F00-3FFF is not configurable, always mapped to the internal palette control.

OAM

In addition, the PPU internally contains 256 bytes of memory known as Object Attribute Memory which determines how sprites are rendered. The CPU can manipulate this memory through memory mapped registers at OAMADDR ($2003), OAMDATA ($2004), and OAMDMA ($4014). OAM can be viewed as an array with 64 entries. Each entry has 4 bytes: the sprite Y coordinate, the sprite tile number, the sprite attribute, and the sprite X coordinate.

Address Low Nibble Description
$0, $4, $8, $C Sprite Y coordinate
$1, $5, $9, $D Sprite tile #
$2, $6, $A, $E Sprite attribute
$3, $7, $B, $F Sprite X coordinate
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