mirror of
https://github.com/tildearrow/furnace.git
synced 2024-11-18 10:35:11 +00:00
55 lines
2.1 KiB
Markdown
55 lines
2.1 KiB
Markdown
# Microchip AY8930
|
|
|
|
a backwards-compatible successor to the AY-3-8910, with increased volume resolution, duty cycle control, three envelopes and highly configurable noise generator.
|
|
|
|
sadly, this soundchip has only ever observed minimal success, and has remained rather obscure since.
|
|
it is best known for being used in the Covox Sound Master, which didn't sell well either. It also observed very minimal success in Merit's CRT-250 machines, but only as a replacement for the AY-3-8910.
|
|
|
|
emulation of this chip in Furnace is now complete thanks to community efforts and hardware testing, which an MSX board called Darky has permitted.
|
|
|
|
# effects
|
|
|
|
- **`12xx`**: set channel duty cycle. `xx` is a value between 00 and 08.
|
|
- `00`: 3.125%
|
|
- `01`: 6.25%
|
|
- `02`: 12.5%
|
|
- `03`: 25%
|
|
- `04`: 50%
|
|
- `05`: 75%
|
|
- `06`: 87.5%
|
|
- `07`: 93.75%
|
|
- `08`: 96.875%
|
|
- **`20xx`**: set channel mode. `xx` may be one of the following:
|
|
- `00`: square
|
|
- `01`: noise
|
|
- `02`: square and noise
|
|
- `03`: envelope
|
|
- `04`: envelope and square
|
|
- `05`: envelope and noise
|
|
- `06`: envelope and square and noise
|
|
- `07`: nothing
|
|
- **`21xx`**: set noise frequency. `xx` is a value between 00 and FF.
|
|
- **`22xy`**: set envelope mode.
|
|
- `x` sets the envelope shape, which may be one of the following:
|
|
- `0: \___` decay
|
|
- `4: /___` attack once
|
|
- `8: \\\\` saw
|
|
- `9: \___` decay
|
|
- `A: \/\/` inverse obelisco
|
|
- `B: \¯¯¯` decay once
|
|
- `C: ////` inverse saw
|
|
- `D: /¯¯¯` attack
|
|
- `E: /\/\` obelisco
|
|
- `F: /___` attack once
|
|
- if `y` is 1 then the envelope will affect this channel.
|
|
- **`23xx`**: set envelope period low byte.
|
|
- **`24xx`**: set envelope period high byte.
|
|
- **`25xx`**: slide envelope period up.
|
|
- **`26xx`**: slide envelope period down.
|
|
- **`27xx`**: set noise AND mask.
|
|
- **`28xx`**: set noise OR mask.
|
|
- **`29xy`**: enable auto-envelope mode.
|
|
- in this mode the envelope period is set to the channel's notes, multiplied by a fraction.
|
|
- `x` is the numerator.
|
|
- `y` is the denominator.
|
|
- if `x` or `y` are 0 this will disable auto-envelope mode.
|