Shiru wrote:
YM2203 is a half channels of YM2612 (Sega Genesis) with minor differences, they are software compatible for the most part and sounds the same.
Actually YM2203 is the original chip that started the OPN family, which is in turn a merge of a "cheapened" OPM (YM2151) core with a SSG (YM2149F which is Yamaha's own version of the legendary AY-3-8910 sound chip from the Intellivision)...
The chip on the Mega Drive in particular is two YM2203 slapped together with some additional interconnection to allow for 4-op voices using the 2 FM cores simultaneously. Ah and SSG stuff got mostly removed keeping only the envelope registers. I suppose, as these are used by the FM synth to enhance the chip features.
There's even tools to translate/convert patches from OPM to OPN or the inverse ... (edit: oy I forgot, you made the tools, Shiru XD my bad)
The VRC7 is a member of the OPL family in the other side, so it uses YM3526 (OPL)/YM3812(OPL2) patches/tones.
The board I posted pictures from contains also an Konami 051649 (SCC) along with it's resistor ladder DAC (051650) allowing for single slot music playback on a MSX computer using Japanese MML compilers such as MGSEL, MuSICA or Performer OPX...
Finally these are pictures of the bottom of the board with the VRC7. The blue board is just a mechanical adapter to allow the connection of a FAKE OPLL (U3567) to a real OPLL connector.
I used a gutted 27512 EPROM "body" as pin carrier for the adapter part as one can notice in the pictures.
Edit 2: I actually fixed the oscillator circuit from the older picture, moved one 27PF and 1Mohm resistors from bottom of the board to the permanent position on top. Resistor is behind the quartz oscillator.
edit: yep... I'm tired of typing the same thing over and over ...