There's a complete list of synth engines used by Casio?

[Brad Saucier]

@silent Was 6 posts in a row necessary? Please don't do that.  You can always edit your post to add more if no one has replied yet.  

[CYBERYOGI =CO=Windler]

Having different pin count means not necessarily a different die inside. Particularly COB, but also other custom ICs were often released in several different package variants (e.g. to fit on different PCBs or to enshroud what they are based on). While the silicon die stays the same, packages can have unused pins omitted or for configuration internally bonded to nearby pins ("bonding options"). Also one of the supply voltage inputs (negative, 0V or positive) often covers the whole bottom of the die; so this pin may be placed anywhere (also as multiple pins among others). Packages that are too large for a particular die sometimes have many pins (often every n-th pin) internally not connected; such NC pins will show high resistance (also in diode test mode) in both directions against all others. Additional pins may be also internally connected to their neighbours. (E.g. FM sound ICs in Chinese keyboards had many additional NC pins to distract from that they were copies of much smaller Yamaha sound ICs. But even Yamaha himself proudly created a "16 pin" sound IC YM3427 with 8 of its pins NC.) To identify camouflage IC variants, it is most important to know that despite possibility of omitting or inserting blank or duplicate pins, the pin order will stay the same (at least unless the die was redesigned too, or a complicated adapter built into the package). Regard that the placement of pin 1 still may differ when the die was installed rotated or the numbering was changed. So it can be a good idea to compare the actual order of function pins around the chip rather than their absolute positions. (Of course this tip is only valid for classic ICs with pin rows along their rims, not modern packages (like BGA or Pentium CPUs) with hundreds of contacts covering their entire bottom.) With COB the pins typically count anticlockwise when looking at the blob side.

 

Of course sometimes type numbers printed on chips are just deceiving to enshroud what is actually inside to complicate hardware piracy.