INES Mapper 076

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iNES Mapper 076 represents NAMCOT-3446, a board used only for the game Megami Tensei: Digital Devil Story.

It rewires the Namcot 108 mapper IC to be able to address 128 KiB of CHR, in exchange for coarser CHR banking.

The PCB also has a 7432 which allows the use of a 28-pin CHR-ROM.

 Registers:
 ---------------------------
 Mask: $E001
 
   $8000:  [.... .AAA]
     A = Address for use with $8001
 
   $8001:  [..DD DDDD]    Data port:
       R:2 ->  CHR reg 0  (2k @ $0000)
       R:3 ->  CHR reg 1  (2k @ $0800)
       R:4 ->  CHR reg 2  (2k @ $1000)
       R:5 ->  CHR reg 3  (2k @ $1800)
       R:6 ->  PRG reg 0  (8k @ $8000)
       R:7 ->  PRG reg 1  (8k @ $a000)
 
 CHR Setup:
 ---------------------------
       $0000   $0400   $0800   $0C00   $1000   $1400   $1800   $1C00 
     +---------------+---------------+---------------+---------------+
     |      R:2      |      R:3      |      R:4      |      R:5      |
     +---------------+---------------+---------------+---------------+
 
 PRG Setup:
 ---------------------------
       $8000   $A000   $C000   $E000  
     +-------+-------+-------+-------+
     |  R:6  |  R:7  | { -2} | { -1} |
     +-------+-------+-------+-------+