NES 2.0 Mapper 394

NES 2.0 Mapper 394 denotes Realtec's HSK007 multicart PCB. Unusually, it can be set to function either as an MMC3 clone or as a J.Y. Company ASIC.

Mode Register ($5009, write)

Mask: unknown, but A3 must be set

D~7654 3210
  ---------
  ...M MCBP
     | |||+- PRG A18
     | ||+-- PRG/CHR A19
     | |+--- CHR A18
     +-+---- Mapper Mode
             0: BNROM
             1: MMC3
             2: J.Y. Company ASIC
             3: Same as 2

Power-on value: $0F

Outer Bank Register ($500B, write)

Mask: unknown, but A3 must be set

D~7654 3210
  ---------
  cC.p PBB.
  || | |++-- PRG A16..A15 in BNROM mode
  || | +---- PRG A17 if p=0
  || +------ PRG A17 in MMC3 mode
  ||          0: From Outer Bank Register (128 KiB inner bank)
  ||          1: From MMC3 (256 KiB inner bank)
  |+-------- CHR A17 if c=0
  +--------- CHR A17 in MMC3 mode
              0: From Outer Bank Register (128 KiB inner bank)
              1: From MMC3 (256 KiB inner bank)

Power-on value: $90

In J.Y. Company ASIC Mode, PRG/CHR A17 always come from the J.Y. Company ASIC.