INES Mapper 076

 Here are Disch's original notes:  
 ========================
 =  Mapper 076          =
 ========================
 
 
 Example Games:
 --------------------------
 Digital Devil Story - Megami Tensei
 
 
 Notes:
 ---------------------------
 PRG Swapping on this mapper defies logic.  I don't know if this is accurate, but it appears to work.
 
 
 Registers:
 ---------------------------
 
 Range,Mask:   $8000-FFFF, $E001
 
 
   $8000:  [.P.. .AAA]
     P = PRG register select (see PRG setup)
     A = Address for use with $8001
 
 
   $8001:  [DDDD 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 or 2  (depending on 'P' bit in $8000)
       R:7 ->  PRG reg 1
 
 
   $A000:  [.... ...M]
     Mirroring:  0=Vert
                 1=Horz
 
 CHR Setup:
 ---------------------------
 
       $0000   $0400   $0800   $0C00   $1000   $1400   $1800   $1C00 
     +---------------+---------------+---------------+---------------+
     |      R:2      |      R:3      |      R:4      |      R:5      |
     +---------------+---------------+---------------+---------------+
 
 
 PRG Setup:
 ---------------------------
 
 R:6 actually seems to access two seperate regs.  Therefore, unlike the typical MMC3-style setup, $8000 and
 $C000 are both independently selectable.  When R:6 is written to, the 'P' bit determines which reg gets
 changed:
 
 P=0:  PRG reg 0  (8k @ $8000 --  "R:6a" below)
 P=1:  PRG reg 2  (8k @ $C000 --  "R:6b" below)
 
       $8000   $A000   $C000   $E000  
     +-------+-------+-------+-------+
     |  R:6a |  R:7  |  R:6b | { -1} |
     +-------+-------+-------+-------+
 
 
 
 Powerup:
 ---------------------------
 
 R:6b seems to be reset to $FE on powerup.  The game does rely on this.