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55 lines
2 KiB
Markdown
55 lines
2 KiB
Markdown
# Microchip AY8930
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a backwards-compatible successor to the AY-3-8910, with increased volume resolution, duty cycle control, three envelopes and highly configurable noise generator.
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sadly, this soundchip has only ever observed minimal success, and has remained rather obscure since.
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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.
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emulation of this chip in Furnace is now complete thanks to community efforts and hardware testing, which an MSX board called Darky has permitted.
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# effects
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- `12xx`: **set channel duty cycle.**
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- `0`: 3.125%
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- `1`: 6.25%
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- `2`: 12.5%
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- `3`: 25%
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- `4`: 50%
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- `5`: 75%
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- `6`: 87.5%
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- `7`: 93.75%
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- `8`: 96.875%
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- `20xx`: **set channel mode.** `xx` may be one of the following:
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- `0`: square
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- `1`: noise
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- `2`: square and noise
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- `3`: envelope
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- `4`: envelope and square
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- `5`: envelope and noise
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- `6`: envelope and square and noise
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- `7`: nothing
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- `21xx`: **set noise frequency.** `xx` is a value between `00` and `FF`.
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- `22xy`: **set envelope mode.**
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- `x` sets the envelope shape, which may be one of the following:
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- `0`: `\___` decay
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- `4`: `/___` attack once
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- `8`: `\\\\` saw
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- `9`: `\___` decay
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- `A`: `\/\/` inverse obelisco
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- `B`: `\¯¯¯` decay once
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- `C`: `////` inverse saw
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- `D`: `/¯¯¯` attack
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- `E`: `/\/\` obelisco
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- `F`: `/___` attack once
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- if `y` is 1 then the envelope will affect this channel.
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- `23xx`: **set envelope period low byte.**
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- `24xx`: **set envelope period high byte.**
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- `25xx`: **slide envelope period up.**
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- `26xx`: **slide envelope period down.**
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- `27xx`: **set noise AND mask.**
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- `28xx`: **set noise OR mask.**
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- `29xy`: **enable auto-envelope mode.**
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- in this mode the envelope period is set to the channel's notes, multiplied by a fraction.
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- `x` is the numerator.
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- `y` is the denominator.
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- if `x` or `y` are 0 this will disable auto-envelope mode.
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