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46 lines
1.9 KiB
Markdown
46 lines
1.9 KiB
Markdown
# General Instrument AY-3-8910
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this chip was used in many home computers (ZX Spectrum, MSX, Amstrad CPC, Atari ST, etc.), video game consoles (Intellivision and Vectrex), arcade boards and even slot machines!
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it is a 3-channel square/noise/envelope sound generator. the chip's powerful sound comes from the envelope...
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the AY-3-8914 variant was used in Intellivision, which is pretty much an AY with 4 level envelope volume per channel and different register format.
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# effects
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- **`20xx`**: set channel mode. `xx` may be one of the following:
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- `00`: square
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- `01`: noise
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- `02`: square and noise
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- `03`: envelope
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- `04`: envelope and square
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- `05`: envelope and noise
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- `06`: envelope and square and noise
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- `07`: nothing
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- **`21xx`**: set noise frequency. `xx` is a value between 00 and 1F.
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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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- **`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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- **`2Exx`**: write to I/O port A.
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- this changes the port's mode to "write". make sure you have connected something to it.
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- **`2Fxx`**: write to I/O port B.
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- this changes the port's mode to "write". make sure you have connected something to it.
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