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furnace/papers/doc/7-systems/nes.md

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NES

the console from Nintendo that plays Super Mario Bros. and helped revive the agonizing video game market in the US during mid-80s.

also known as Famicom. It is a five-channel PSG: first two channels play pulse wave with three different duty cycles, third is a fixed-volume triangle channel, fourth is a noise channel (can work in both pseudo-random and periodic modes) and fifth is a (D)PCM sample channel.

effects

  • 11xx: write to delta modulation counter.
    • this may be used to attenuate the triangle and noise channels.
    • will not work if a sample is playing.
  • 12xx: set duty cycle or noise mode of channel.
    • may be 0-3 for the pulse channels and 0-1 for the noise channel.
  • 13xy: setup sweep up.
    • x is the time.
    • y is the shift.
    • set to 0 to disable it.
  • 14xy: setup sweep down.
    • x is the time.
    • y is the shift.
    • set to 0 to disable it.
  • 18xx: set PCM channel mode.
    • 00: PCM (software).
    • 01: DPCM (hardware).
    • when in DPCM mode, samples will sound muffled (due to its nature), availables pitches are limited and loop point is ignored.