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[[File:crt_pcm.jpg|right|thumb|NEO-PCM chip found in a MVS cartridge. Picture courtesy of [[http://www.mvs-scans.com MVS-Scans]].]]
{{ChipInfo
|picture=crt_pcm.jpg
|pkg=QFP80R
|manu=fujitsu
|date=1992 ?
|gates=
|used_on=[[Cartridges]]
}}


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" probably because it was used in some SNK claw cranes) is a {{Chipname|V ROM}} banking and demultiplexing chip, found in AES and MVS [[cartridges]], and on [[ROM-Only boards|ROM-only]] arcade boards.


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 boards|ROM-only]] arcade boards. Used to demultiplex V ROM (ADPCM-A and ADPCM-B) data from mixed-content ROM chips.
Early cartridges had separate [[YM2610|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.


[[NEO-PCM2]] can also be found in late cartridges and with [[NEO-YSA2]].
{{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 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 4-bit counter on {{Sig|68KCLKB|68KCLKB}} for synchronisation.
Uses several latches for address and data, as well as a counter clocked by {{Sig|68KCLKB|68KCLKB}} for synchronisation.


=Internal logic=
=Internal logic=


Takes advantage of the asynchronous reading from the [[YM2610]]. See [[YM2610 bus timing]].
The trick takes advantage of the asynchronous and predictable access to the ADPCM-A and APDCM-B data by the {{Chipname|YM2610}}. See [[YM2610 bus timing]].


Verilog: todo.
[[https://github.com/neogeodev/SNKVerilog/tree/master/PCM Verilog definition]].


=Pinout=
=Pinout=


[[File:Pcm_pinout.png|512px]]
{{Pinout|PCM|640}}


OpenOffice Draw file: [[File:pcm.odg]]
*INVIN, INVOUT: Simple inverter


Has an inverting gate on pins 26 and 27.
*SDPOE, SDROE, SDPMPX, SDRMPX: from the YM2610
 
*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


*V D0~V D7: V ROM(s) data bus
*V D0~V D7: V ROM(s) data bus
*V A-1~V A22: V ROM(s) address 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).


[[Category:Chips]]
[[Category:Chips]]

Latest revision as of 14:00, 8 December 2020

Package QFP80R
Manufacturer
First use 1992 ?
Used on Cartridges

PCM (not "NEO-PCM" probably because it was used in some SNK claw cranes) is a V ROM banking and demultiplexing chip, found in AES and MVS cartridges, and on ROM-only arcade boards.

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.

NEO-PCM2 can also be found in late cartridges, and with NEO-YSA2.

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.

Internal logic

The trick takes advantage of the asynchronous and predictable access to the ADPCM-A and APDCM-B data by the YM2610. See YM2610 bus timing.

[Verilog definition].

Pinout


Edit this pinout

  • 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).