|First use||1992 ?|
Early cartridges had separate ADPCM-A and ADPCM-B sound ROMs. Since one was often emptier than the other, SNK devised a way to mix both types in the same ROM chip to save space and reduce costs.
On some Cartridge boards, VA20~VA22 are used to select which of the 4 possible V ROMs to use (decoded by a LS139).
Uses several latches for address and data, as well as a counter clocked by 68KCLKB for synchronisation.
- INVIN, INVOUT: Simple inverter
- SDPOE, SDROE, SDPMPX, SDRMPX: from the YM2610
- SDRAD0~SDRAD7: ADPCM-A multiplexed bus part
- SDPAD0~SDPAD7: ADPCM-B multiplexed bus part
- SDRA8, SDRA9, SDRA20~SDRA23: ADPCM-A address bus
- SDPA8~SDPA11: ADPCM-B address bus
- V D0~V D7: V ROM(s) data bus
- V A-1~V A22: V ROM(s) address bus
- When the MODE pin is low, V A19~V A22 become 4 active-low decoded outputs (based on value from the internal V A19 and V A20).