PCM



V ROM banking and multiplexing chip, found in AES and MVS cartridges, and on ROM-only arcade boards. Used to multiplex V ROM (ADPCM-A and ADPCM-B) access to mixed-content ROM chips.

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

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).

=Internal logic=

Takes advantage of the asynchronous reading from the YM2610. See YM2610 bus timing.

Verilog: todo.

=Pinout=



OpenOffice Draw file:

Has an inverting gate 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