YM2612
From Sega Retro
YM2612 is a 6 channel FM synthesis (Frequency Modulation) sound synthesizer integrated circuit produced by Yamaha. It belongs to a family of Yamaha FM synthesizer chips, and can be considered an ancestor to the OPL2 (YM3812) and OPL (YMF262) FM ICs that were used in the popular AdLib and Creative Labs SoundBlaster PC soundcards.
The Yamaha YM 2612 FM Synthesis Chip is based on the Yamaha 2151 (which was used in earlier Sega Arcade Games). Ironically, it's of a higher quality then the OPL2/3 FM Synthesis chips produced by Yamaha and used in Creative Labs PC sound cards such as the popular "Sound Blaster" line.
The YM2612 was notably used in the Sega Genesis game console and has the following features:
- Six concurrent FM channels (or voices)
- The sixth channel can be used as an FM or DAC channel (but not both)
- Four operators per channel
- Two timers
- A low frequency oscillator
- Stereo output
Each channel may be assigned to either left, right or both (centre) of the stereo output.
The special sixth channel can act as a DAC (Digital to Analogue Converter) by means of the 'DAC Enable' register, this allows the chip to play 8-bit PCM sound samples. Enabling the DAC disables the FM for that channel. Data is written to the DAC via an 8-bit register. The YM2612 does not provide any timing or buffering of the PCM samples, so all frequency control and buffering must be done in software by the host processor.
The synth patches used by the YM2612 in Mega Drive games are compatible with certain members of the Yamaha DX/TX synthesizers, such as the DX100.