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# 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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Furnace is capable of doing software sample playback on AY-3-8910, where all 3 channels can play 4-bit PCM samples (at the cost of a very high CPU usage) and utilize CPU timer effects, providing all kinds of modulation (PWM and envelope distortion) effects, again at the cost of a higher CPU usage. Songs utilizing timer effects may not sound as intented after VGM export.
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## effects
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- `20xx` : **set channel mode.**
- `0` : square
- `1` : noise
- `2` : square and noise
- `3` : envelope
- `4` : envelope and square
- `5` : envelope and noise
- `6` : envelope and square and noise
- `7` : nothing
- `21xx` : **set noise frequency.** range is `0` to `1F` .
- `22xy` : **set envelope mode.**
- `x` sets the envelope shape:
- `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
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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.**
- `24xx` : **set envelope period high byte.**
- `25xx` : **slide envelope period up.**
- `26xx` : **slide envelope period down.**
- `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.
- `x` is the numerator.
- `y` is the denominator.
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- if `x` or `y` are 0 this will disable auto-envelope mode.
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- `2Cxx` : **set timer period offset.**
- bit 7 is the sign.
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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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## what is obelisco
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it's a name I use for a spiky waveform that starts low.
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its origin is a wavetable that comes in DefleMask that happens to be called Obelisco.
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## AY derivative modes
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AY-3-810 was an absurdly popular chip that was blessed with many third-party clones, licensed or not.
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- the AY-3-8914 variant was used in Intellivision, which is pretty much an 8910 with 4 level envelope volume per channel and different register format.
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- Yamaha YM2149 was an AY-3-8910 clone released in 1983. it's almost identical to AY with minor differences being: higher hardware envelope step resolution (16 vs 32), half-clock mode when voltage level is low, much stronger DC offset and cleaner, but softer output.
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- Sunsoft 5B is YM2149 clone with half-clock mode forced on.
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## info
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this chip uses the [AY-3-8910 ](../4-instrument/ay8910.md ) instrument editor.
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## chip config
the following options are available in the Chip Manager window:
- **Clock rate**: sets the rate at which the chip will run.
- **Chip type**: changes the chip model.
- AY-3-8910: the original model.
- YM2149(F): Yamaha clone with higher envelope resolution and a different volume curve.
- Sunsoft 5B: a special model found in one of Sunsoft's Famicom cartridges.
- AY-3-8914: scrambled registers. has envelope volume control.
- **Stereo**: enable stereo output. channel 1 is output left, channel 2 is output center and channel 3 is output right.
- **Separation**: allows you to set left/right separation.
- **Half Clock divider**: pulls the half clock pin, running the chip at half the speed.
- only available in YM2149.
