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

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.