furnace/papers/doc/7-systems/ym2610b.md
2022-03-22 00:58:07 -05:00

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# Taito Arcade/Yamaha YM2610B
YM2610B is basically YM2610 with 2 extra FM channels used at some 90s Taito arcade hardware.
it is backward compatible with the original chip.
# 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 mutliplier.
- `18xx`: toggle extended channel 2 mode.
- 0 disables it and 1 enables it.
- only in extended channel 2 system.
- `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. `xx` may be one of the following:
- `00`: square
- `01`: noise
- `02`: square and noise
- `03`: nothing (apparently)
- `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 1F.
- `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.
- `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.