furnace/papers/doc/7-systems/ym2203.md

Yamaha YM2203 (OPN)

a cost-reduced version of the YM2151 (OPM). it only has 3 FM channels instead of 8 and removes the LFO.

however it does contain an AY/SSG part which provides 3 channels of square wave with noise and envelope.

this chip was used in the PC-88/PC-98 series of computers, and in some arcade boards.

several variants of this chip were released as well, with more features.

effects

• 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 3 mode.
  • 0 disables it and 1 enables it.
  • only in extended channel 3 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.
• 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.