PCM: Difference between revisions

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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]]
}}


[[V ROM]] banking and multiplexing chip, found in AES and MVS [[cartridges]].
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.


[[NEO-PCM2]] can also be found in late cartridges and with [[NEO-YSA2]] on [[ROM-Only boards|ROM-only]] arcade boards.
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.


On some [[cartridge boards]], V A20~V A22 can be used to select which of the 4 possible V ROMs to use (decoded by a LS139).
{{Chipname|NEO-PCM2}} can also be found in late cartridges, and with {{Chipname|NEO-YSA2}}.
 
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 counter clocked by {{Sig|68KCLKB|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 {{Chipname|YM2610}}. See [[YM2610 bus timing]].
 
[[https://github.com/neogeodev/SNKVerilog/tree/master/PCM Verilog definition]].


=Pinout=
=Pinout=


[[File:Pcm_pinout.png]]
{{Pinout|PCM|640}}
 
*INVIN, INVOUT: Simple inverter


Not sure about A19.
*SDPOE, SDROE, SDPMPX, SDRMPX: from the YM2610
*SDPOE, SDROE, SDPMPX, SDRMPX: from the [[YM2610]]


*SDRAD0~SDRAD7: ADPCM-A data bus
*SDRAD0~SDRAD7: ADPCM-A multiplexed bus part
*SDPAD0~SDPAD7: ADPCM-B data bus
*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 A0~V A21: 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).