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furnace/doc/7-systems/nes.md
Electric Keet a9d4bf1fdc Accurate number! 
Well, accurate enough.
2023-06-30 20:41:16 -07:00

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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 sound generator: 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. range is 00 to 7F.
    • this may be used to attenuate the triangle and noise channels; at 7F, they will be at about 57% volume.
    • will not work if a sample is playing.
  • 12xx: set duty cycle or noise mode of channel.
    • may be 0 to 3 for the pulse channels:
      • 0: 12.5%
      • 1: 25%
      • 2: 50%
      • 3: 75%
    • may be 0 or 1 for the noise channel:
      • 0: long (15-bit LFSR, 32767-step)
      • 1: short (9-bit LFSR, 93-step)
  • 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.
  • 15xx: set envelope mode.
    • 0: envelope + length counter. volume represents envelope duration.
    • 1: length counter. volume represents output volume.
    • 2: looping envelope. volume represents envelope duration.
    • 3: constant volume. default value. volume represents output volume.
    • Pulse and noise channels only.
    • you may need to apply a phase reset (using the macro) to make the envelope effective.
  • 16xx: set length counter.
    • see table below for possible values.
    • this will trigger phase reset.
  • 17xx: set frame counter mode.
    • 0: 4-step.
      • NTSC: 120Hz sweeps and lengths; 240Hz envelope.
      • PAL: 100Hz sweeps and lengths; 200Hz envelope.
      • Dendy: 118.9Hz sweeps and lengths; 237.8Hz envelope.
    • 1: 5-step.
      • NTSC: 96Hz sweeps and lengths; 192Hz envelope.
      • PAL: 80Hz sweeps and lengths; 160Hz envelope.
      • Dendy: 95.1Hz sweeps and lengths; 190.2Hz envelope.
  • 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.
  • 19xx: set triangle linear counter.
    • 00 to 7F set the counter.
    • 80 and higher halt it.
  • 20xx: set DPCM frequency.
    • only works in DPCM mode.
    • see table below for possible values.

tables

short noise frequencies (NTSC)

note arpeggio fundamental MIDI note pitch
C-0 @0 4.7 Hz -9.47 d_1 + 53¢
C#0 @1 9.5 Hz 2.53 D-0 + 53¢
D-0 @2 18.9 Hz 14.55 D-1 + 55¢
D#0 @3 25.3 Hz 19.53 G-1 + 53¢
E-0 @4 37.9 Hz 26.55 D-2 + 55¢
F-0 @5 50.6 Hz 31.57 G-2 + 57¢
F#0 @6 75.8 Hz 38.55 D-3 + 55¢
G-0 @7 95.3 Hz 42.51 F#3 + 51¢
G#0 @8 120.3 Hz 46.55 A#3 + 55¢
A-0 @9 150.4 Hz 50.41 D-4 + 41¢
A#0 @10 200.5 Hz 55.39 G-4 + 39¢
B-0 @11 300.7 Hz 62.41 D-5 + 41¢
C-1 @12 601.4 Hz 74.41 D-6 + 41¢
C#1 @13 1202.8 Hz 86.41 D-7 + 41¢
D-1 @14 2405.6 Hz 98.41 D-8 + 41¢
D#1 @15 4811.2 Hz 110.41 D-9 + 41¢

reference: NESdev

length counter table

value raw NTSC PAL Dendy NTSC 5-step PAL 5-step Dendy 5-step
03 2 17ms 20ms 17ms 21ms 25ms 21ms
05 4 33ms 40ms 34ms 42ms 50ms 42ms
07 6 50ms 60ms 50ms 63ms 75ms 63ms
09 8 67ms 80ms 67ms 83ms 100ms 84ms
00 10 83ms 100ms 84ms 104ms 125ms 105ms
0B 10 83ms 100ms 84ms 104ms 125ms 105ms
0D 12 100ms 120ms 101ms 125ms 150ms 126ms
10 12 100ms 120ms 101ms 125ms 150ms 126ms
0C 14 117ms 140ms 118ms 146ms 175ms 147ms
0F 14 117ms 140ms 118ms 145ms 175ms 147ms
1C 16 133ms 160ms 135ms 167ms 200ms 168ms
11 16 133ms 160ms 135ms 167ms 200ms 168ms
13 18 150ms 180ms 151ms 188ms 225ms 189ms
02 20 166ms 200ms 168ms 208ms 250ms 210ms
15 20 167ms 200ms 168ms 208ms 250ms 210ms
17 22 183ms 220ms 185ms 229ms 275ms 231ms
12 24 200ms 240ms 202ms 250ms 300ms 252ms
19 24 200ms 240ms 202ms 250ms 300ms 252ms
0E 26 217ms 260ms 219ms 271ms 325ms 273ms
1B 26 217ms 260ms 219ms 271ms 325ms 273ms
1D 28 233ms 280ms 235ms 292ms 350ms 294ms
1F 30 250ms 300ms 252ms 313ms 375ms 315ms
1E 32 267ms 320ms 269ms 333ms 400ms 336ms
04 40 333ms 400ms 336ms 417ms 500ms 421ms
14 48 400ms 480ms 404ms 500ms 600ms 505ms
0A 60 500ms 600ms 505ms 625ms 750ms 631ms
1A 72 600ms 720ms 606ms 750ms 900ms 757ms
06 80 667ms 800ms 673ms 833ms 1.0s 841ms
16 96 800ms 960ms 807ms 1.0s 1.2s 1.0s
08 160 1.3s 1.6s 1.3s 1.7s 2.0s 1.7s
18 192 1.6s 1.9s 1.6s 2.0s 2.4s 2.0s
01 254 2.1s 2.5s 2.1s 2.6s 3.2s 2.7s

reference: NESdev

DPCM frequency table

value NTSC PAL
00 4181.7Hz 4177.4Hz
01 4709.9Hz 4696.6Hz
02 5264.0Hz 5261.4Hz
03 5593.0Hz 5579.2Hz
04 6257.9Hz 6023.9Hz
05 7046.3Hz 7044.9Hz
06 7919.3Hz 7917.2Hz
07 8363.4Hz 8397.0Hz
08 9419.9Hz 9446.6Hz
09 11186.1Hz 11233.8Hz
0A 12604.0Hz 12595.5Hz
0B 13982.6Hz 14089.9Hz
0C 16884.6Hz 16965.4Hz
0D 21306.8Hz 21315.5Hz
0E 24858.0Hz 25191.0Hz
0F 33143.9Hz 33252.1Hz