VRC7 audio

VRC7 Audio

The Konami VRC7, in addition to being a mapper chip, also produces 6 channels of 2-operator FM Synthesis Audio. The synthesis core appears to be mostly compatible with the Yamaha YM2413 OPLL:

• Register layout is the same
• VRC7 has 6 channels, OPLL has 9
• VRC7 has no rhythm channels, OPLL does (the last 3 channels are either FM or Rhythm on OPLL)
• VRC7 built-in instruments are NOT the same as OPLL instruments (except for instruments 4,5,7,8 which are probably the same on both)
• VRC7 has no readily-accessible status register, under normal circumstances it is write-only; OPLL has an undocumented, 2-bit 'internal state' register.
• VRC7 has an internal state output pin (may be serial version of the 2 bit internal state register) and has one output pin for audio, multiplexed for all 6 channels; OPLL has two output pins, one for FM and one for Rhythm, and has no special status pin.

The VRC7 Registers are located at $9010 and $9030

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