CMOS version of OPN.
Spec
3ch of FM(4op), 3ch of SSG.
Bespoke for NEC and their 3rd party
TQFP64
EPSON PC-486/586 series
Several sound options for PC-9801 series.
http://www.geocities.co.jp/SiliconValley-Cupertino/4294/sound/ymf264.htm