Introduction to NES graphics Don Miller / NO CARRIER PlayPower.org Platform Education Director

Introduction  The $10 Computer & NES  Introduction to NES graphics › NES Background Information › NES PPU (Picture Processing Unit) ‏

The $10 Computer & NES The PlayPower $10 Computer is a clone of the popular 8-bit Nintendo NES. There are some differences, but they run the same software.

 The NES CPU core is based on the 6502 processor and runs at approximately 1.79 MHz (1.66 MHz in a PAL NES).  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.

 The PPU (Picture Processing Unit), more specifically known as Ricoh RP2C02 (NTSC version) / RP2C07 (PAL version), is the microprocessor in the NES responsible for generating video signals from graphic data stored in memory.

 The chip is known for its effective use of memory, using very little memory to store graphical data.  It was rather advanced for its time when the Famicom (Japanese version of the NES) was released, sporting full sprite support, movable backgrounds, and many colors on screen at the same time.

 Picture resolution of 256 × 240 pixels (fully visible on PAL, but cropped to 256 × 224 on most NTSC television sets) ‏  2KB external RAM for graphics information storage  Up to 64 sprites (movable objects) on screen simultaneously (only 8 visible per scan line) ‏  256 bytes for sprite data storage  8 × 8 or 8 × 16 (selectable) sized sprite tiles  Two 4KB tile sets with space for 256 tiles each  32 bytes for palette storage  25 colors simultaneously from a hardware color palette of 64 colors

Picture resolution of 256 × 240 pixels  The NES screen is made of 8x8 pixel background tiles.  That means the NES screen is 32x30 tiles.  The magic number: 32 * 30 = 960.

Two 4kb tile sets with space for 256 tiles each  Even the most basic NES game (think SMB or Balloon Fight) has 8kb for graphics data storage.  4kb in one tile set, for background  4kb in another tile set, for the sprites  Load up YY-CHR to show SMB

32 bytes for palette storage  The NES palette storages used one byte for each color stored.  16 bytes for the background  16 bytes for the sprites  Here is an example of the NES palette:

25 colors simultaneously  The NES palette is 64 total colors.  From the 32 colors chosen for background and sprites, only 25 can be shown simultaneously.  This is because the first color repeats every four colors, and is the transparent/background color.  Example:  $0f, $30, $16, $29, $0f, $10, $39, $30  Load up Nintendulator to show 25 color limit

Early games  Early games didn’t use a mapper, and only included a few chips on the main board:

Programs and Compilers  Programs I like to use: › YY-CHR (freeware tile editor) › XVI32 (freeware hex editor) › Pin Eight nametable editor: name.exe › Loopy's ASM6 compiler (for 6502 ASM language) ‏ › Context (with 6502 ASM highlighter) › Nestopia and Nintendulator (accurate NES emulators)

Programs and Compilers  Programs I like to use: › YY-CHR (freeware tile editor) › XVI32 (freeware hex editor) › Pin Eight nametable editor: name.exe › Loopy's ASM6 compiler (for 6502 ASM language) ‏ › Context (with 6502 ASM highlighter) › Nestopia and Nintendulator (accurate NES emulators)