furnace/doc/7-systems/ym2610.md
Electric Keet 81ab2acb2c Lots of little cleanup.
Trying for more consistency and clarity, especially for quick reference.
2023-06-25 00:05:30 -07:00

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# Neo Geo/Yamaha YM2610
originally an arcade board, but SNK shortly adapted it to a rather expensive video game console with the world's biggest cartridges because some people liked the system so much they wanted a home version of it.
its soundchip is a 4-in-1: 4ch 4-op FM, YM2149 (AY-3-8910 clone) and 2 different format ADPCM in a single package!
# effects
- `10xy`: **set LFO parameters.**
- `x` toggles the LFO.
- `y` sets its speed.
- `11xx`: **set feedback of channel.**
- `12xx`: **set operator 1 level.**
- `13xx`: **set operator 2 level.**
- `14xx`: **set operator 3 level.**
- `15xx`: **set operator 4 level.**
- `16xy`: **set multiplier of operator.**
- `x` is the operator (1-4).
- `y` is the multiplier.
- `18xx`: **toggle extended channel 2 mode.**
- 0 disables it and 1 enables it.
- only in extended channel 2 chip.
- `19xx`: **set attack of all operators.**
- `1Axx`: **set attack of operator 1.**
- `1Bxx`: **set attack of operator 2.**
- `1Cxx`: **set attack of operator 3.**
- `1Dxx`: **set attack of operator 4.**
- `20xx`: **set SSG channel mode.**
- `0`: square
- `1`: noise
- `2`: square and noise
- `3`: nothing (apparently)
- `4`: envelope and square
- `5`: envelope and noise
- `6`: envelope and square and noise
- `7`: nothing
- `21xx`: **set noise frequency.** range is `00` 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
- 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.**
- `29xy`: **enable SSG 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.
- `30xx`: **enable envelope hard reset.**
- this works by inserting a quick release and tiny delay before a new note.
- `50xy`: **set AM of operator.**
- `x` is the operator (1-4). a value of 0 means "all operators".
- `y` determines whether AM is on.
- `51xy`: **set SL of operator.**
- `x` is the operator (1-4). a value of 0 means "all operators".
- `y` is the value.
- `52xy`: **set RR of operator.**
- `x` is the operator (1-4). a value of 0 means "all operators".
- `y` is the value.
- `53xy`: **set DT of operator.**
- `x` is the operator (1-4). a value of 0 means "all operators".
- `y` is the value:
- 0: +0
- 1: +1
- 2: +2
- 3: +3
- 4: -0
- 5: -3
- 6: -2
- 7: -1
- `54xy`: **set RS of operator.**
- `x` is the operator (1-4). a value of 0 means "all operators".
- `y` is the value.
- `55xy`: **set SSG-EG of operator.**
- `x` is the operator (1-4). a value of 0 means "all operators".
- `y` is the value (0-8).
- values between 0 and 7 set SSG-EG.
- value 8 disables it.
- `56xx`: **set DR of all operators.**
- `57xx`: **set DR of operator 1.**
- `58xx`: **set DR of operator 2.**
- `59xx`: **set DR of operator 3.**
- `5Axx`: **set DR of operator 4.**
- `5Bxx`: **set D2R/SR of all operators.**
- `5Cxx`: **set D2R/SR of operator 1.**
- `5Dxx`: **set D2R/SR of operator 2.**
- `5Exx`: **set D2R/SR of operator 3.**
- `5Fxx`: **set D2R/SR of operator 4.**