Before the basics

From NESdev Wiki
Jump to navigationJump to search


A digital computer, such as a PC or NES, is filled with millions of tiny switches that can be turned on or off. Some switches store information for short time; these are called memory. Other switches calculate things based on the output of other switches; these are called logic. Each switch can be on or off, representing true or false, or the numbers 1 or 0. Multiple switches grouped together can represent larger values. A CPU reads machine code from a memory and treats it as instructions to perform arithmetic and logic operations on other values in memory or to perform input and output. Some of the input and output involve user interaction: the user gives commands to the computer, and the computer displays the result.

If you're confused, now is the opportunity to become familiar with the following basic concepts from computer engineering and computer science. These articles from Wikipedia are in English, and many have been translated into other languages.

More advanced topics

It has been suggested that understanding these topics is not necessary to program low-complexity games in assembly language without sound, such as a workalike of Magnavox Odyssey tennis. They are held here for forthcoming sorting into a separate page.

Introducing the NES

The Nintendo Entertainment System has the following components:

  • 2A03 CPU IC made by Ricoh
    • CPU based on the MOS Technology 6502 8-bit microprocessor
    • serial input for game controllers
    • audio output comprising four tone generators and a delta modulation playback device
  • 2 KiB of RAM for use by the CPU
  • 2C02 PPU (picture processing unit)
    • tile-based background image
    • 64 sprites (individually moving objects)
    • 25 colors out of 53
    • 256x240 pixel progressive picture generator
    • NTSC color encoder
  • 2 KiB of RAM for use by the PPU

Cartridges have the following components:

  • 16 KiB or more PRG ROM, for use by the CPU
  • 8 KiB or more CHR ROM or CHR RAM, for use by the PPU (and in some cases by the CPU)
  • (optional) Bank switching hardware for the ROMs
  • (optional) Logic to generate interrupts

External links