PCM: Difference between revisions
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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 reduce cost. | 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 reduce cost. | ||
PCM (not "'''NEO'''-PCM" for some reason) is a | PCM (not "'''NEO'''-PCM" for some reason) is a {{Chipname|V ROM}} banking and demultiplexing chip, found in AES and MVS [[cartridges]], and on [[ROM-Only boards|ROM-only]] arcade boards. Used to demultiplex V ROM (ADPCM-A and ADPCM-B) data from mixed-content ROM chips. | ||
{{Chipname|NEO-PCM2}} can also be found in late cartridges and with {{Chipname|NEO-YSA2}}. | |||
On some [[:Category:cartridge boards|Cartridge boards]], VA20~VA22 can be used to select which of the 4 possible V ROMs to use (decoded by a LS139). | On some [[:Category:cartridge boards|Cartridge boards]], VA20~VA22 can be used to select which of the 4 possible V ROMs to use (decoded by a LS139). | ||
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=Internal logic= | =Internal logic= | ||
Takes advantage of the asynchronous reading from the | Takes advantage of the asynchronous reading from the {{Chipname|YM2610}}. See [[YM2610 bus timing]]. | ||
Verilog: | Verilog: to do. | ||
=Pinout= | =Pinout= | ||
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OpenOffice Draw file: [[File:pcm.odg]] | OpenOffice Draw file: [[File:pcm.odg]] | ||
Has an | Has an inverter on pins 26 and 27. | ||
*SDPOE, SDROE, SDPMPX, SDRMPX: from the | *SDPOE, SDROE, SDPMPX, SDRMPX: from the YM2610. | ||
*SDRAD0~SDRAD7: ADPCM-A multiplexed bus part | *SDRAD0~SDRAD7: ADPCM-A multiplexed bus part | ||
*SDPAD0~SDPAD7: ADPCM-B multiplexed bus part | *SDPAD0~SDPAD7: ADPCM-B multiplexed bus part | ||
*SDRA8,SDRA9,SDRA20~SDRA23: ADPCM-A address bus | *SDRA8, SDRA9, SDRA20~SDRA23: ADPCM-A address bus | ||
*SDPA8~SDPA11: ADPCM-B address bus | *SDPA8~SDPA11: ADPCM-B address bus | ||
Revision as of 01:47, 16 January 2016
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 reduce cost.
PCM (not "NEO-PCM" for some reason) is a V ROM banking and demultiplexing chip, found in AES and MVS cartridges, and on ROM-only arcade boards. Used to demultiplex V ROM (ADPCM-A and ADPCM-B) data from mixed-content ROM chips.
NEO-PCM2 can also be found in late cartridges and with NEO-YSA2.
On some Cartridge boards, VA20~VA22 can be 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 4-bit counter on 68KCLKB for synchronisation.
Internal logic
Takes advantage of the asynchronous reading from the YM2610. See YM2610 bus timing.
Verilog: to do.
Pinout
OpenOffice Draw file: File:Pcm.odg
Has an inverter on pins 26 and 27.
- 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