NES 2.0 Mapper 528

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NES 2.0 Mapper 528 is used for the 1995 New Series Super 2-in-1 multicart (title screen: Rugby 2-in-1), containing both of Sunsoft's Dodge Danpei games. Its UNIF board name is UNL-831128C. Although the ROM image's common name is "1995 New Series Super 2-in-1 (Unl,Vrc7p)", only the IRQ counter functions like the VRC7's; the other registers are more like Sunsoft's FME-7.

Registers

Game select ($A00x/C00x)

A~FEDC BA98 7654 3210
  -------------------
  1G.. .... .... ....
   +------------------ Select game
                        0: Dodge Danpei
                        1: Dodge Danpei 2

FME-7-compatible registers ($A000-A00C/$C000-$C00C)

These registers function like the Sunsoft FME-7's registers $0-$C (excluding $8 and $B), except that A0-A3 select the register directly; there is no index register. Register $B is not functional, as the CPU $C000-$DFFF is hard-wired to the second-to-last bank (unlike the FME-7), and CPU $E000-$FFFF hard-wired to the last bank (as on the FME-7).

$A000: Set 1 KiB CHR-ROM bank at PPU $0000-$03FF
$A001: Set 1 KiB CHR-ROM bank at PPU $0400-$07FF
$A002: Set 1 KiB CHR-ROM bank at PPU $0800-$0BFF
$A003: Set 1 KiB CHR-ROM bank at PPU $0C00-$0FFF
$A004: Set 1 KiB CHR-ROM bank at PPU $1000-$13FF
$A005: Set 1 KiB CHR-ROM bank at PPU $1400-$17FF
$A006: Set 1 KiB CHR-ROM bank at PPU $1800-$1BFF
$A007: Set 1 KiB CHR-ROM bank at PPU $1C00-$1FFF
$A008: See below.
$A009: Set 8 KiB PRG-ROM bank at CPU $8000-$9FFF
$A00A: Set 8 KiB PRG-ROM bank at CPU $A000-$BFFF
$A00B: No function
$A00C: Select nametable mirroring type (V/H/S0/S1).

PRG $6000-$7FFF control ($A008/$C008)

This register seems to be a simplified version of the FME-7's register $8. Value $01 selects PRG-RAM, all other values select an 8 KiB PRG-ROM bank at CPU $6000-$7FFF.

VRC-compatible IRQ ($A00D-$A00F/$C00D-$C00F)

$A00D/$C00D: IRQ Control
$A00E/$C00E: IRQ Acknowledge
$A00F/$C00F: IRQ Latch.

See VRC IRQ for details.

Notes

Note that the first Dodge Danpei game only has 128 KiB of PRG-ROM while the second has 256 KiB, requiring careful application of PRG-ROM base offsets and masks. Although the commonly-available UNIF ROM image only has one PRG chunk, it is highly likely that the cartridge used two PRG-ROM chips.