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SNES Hardware Overview

Understanding SNES hardware is essential for effective game development.

Contents

Document Description
Memory Map RAM, ROM, and register layout
Registers Complete hardware register reference
OAM Sprite attribute memory documentation

For graphics (PPU, tiles, modes, palettes), see the SNES Graphics Guide. For audio (SPC700, DSP, BRR, SNESMOD), see the SNES Sound Guide.

Quick Reference

Specifications

Component Specification
CPU 65816 @ 3.58 MHz (NTSC) / 3.55 MHz (PAL)
Work RAM 128 KB
VRAM 64 KB
OAM 544 bytes (128 sprites + size/position bits)
CGRAM 512 bytes (256 colors x 2 bytes)
APU SPC700 @ 1.024 MHz + DSP
Audio RAM 64 KB

Resolution

Mode Resolution
NTSC 256x224 or 256x239
PAL 256x239 or 256x268
Hi-res 512x224 (limited use)

Colors

  • 15-bit color (32768 colors)
  • 256 simultaneous colors (8 palettes x 16 colors for BG, same for sprites)
  • Format: 0BBBBBGGGGGRRRRR

Key Concepts

Vertical Blank (VBlank)

The PPU draws the screen line by line. VBlank is the period when the PPU is not drawing (returning to top of screen). This is the only safe time to update VRAM, OAM, and CGRAM.

// Wait for VBlank before updating graphics
WaitForVBlank();
// Now safe to DMA to VRAM
WaitForVBlank
void WaitForVBlank(void)
Wait for next VBlank period.

Tiles and Sprites

Tiles are 8x8 pixel graphics used for both backgrounds and sprites.

Sprites (Objects/OBJ) are movable graphics composed of one or more tiles:

  • 128 sprites maximum
  • Sizes: 8x8, 16x16, 32x32, 64x64
  • 32 sprites per scanline limit
  • Can be flipped horizontally/vertically

Background Modes

Mode BG1 BG2 BG3 BG4 Colors
0 4 4 4 4 4 per BG
1 16 16 4 - Common
2 16 16 - - Per-tile offset
3 256 16 - - Direct color
4 256 4 - - Per-tile offset
5 16 4 - - Hi-res
6 16 - - - Hi-res + offset
7 256 - - - Mode 7 rotation

Most games use Mode 1 (good balance of features).

Banks and Addressing

The 65816 has a 24-bit address space divided into 256 "banks" of 64KB each:

$00:0000 - $00:FFFF Bank 0 (direct page, stack, I/O)
$7E:0000 - $7E:FFFF Work RAM (low 64KB)
$7F:0000 - $7F:FFFF Work RAM (high 64KB)
$80:0000 - $FF:FFFF ROM and mirrors

LoROM vs HiROM

ROM mapping modes affect how cartridge ROM appears in the address space:

Mode ROM Start Max Size Common Use
LoROM $80:8000 4 MB Most games
HiROM $C0:0000 4 MB Large games
ExHiROM Varies 8 MB Very large games

OpenSNES uses LoROM by default.

Further Reading