INES Mapper 040

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iNES Mapper 040 describes one of Whirlwind Manu's successful attempts (verified cartridge number LF36) at converting the Japanese version of Super Mario Bros. 2 from the FDS to a cartridge. Their first attempt (cartridge number LE10, NES 2.0 Mapper 304) hangs on real hardware after completing level 4-4.

This description was produced from the source code of FCEUX and Nestopia.

 Registers:
 ---------------------------
 Range,Mask:   $8000-FFFF, $E000

   $8000:  Disable and acknowledge IRQ
   $A000:  Enable IRQ
   $E000:  8 KiB bank mapped at $C000
 
 PRG Setup:
 ---------------------------
 
       $6000   $8000   $A000   $C000   $E000  
     +-------+-------+-------+-------+-------+
     | { 6 } | { 4 } | { 5 } | $E000 | { 7 } |
     +-------+-------+-------+-------+-------+

Like mapper 50, this hardware produces an interrupt 4096 M2 cycles after the IRQ is enabled.

The corresponding hardware is a CD4020 functioning as a 13-bit counter, and if the software doesn't acknowledge the interrupt for another 4096 cycles it will self-acknowledge.

See also