INES Mapper 052

 Here are Disch's original notes:  
 ========================
 =  Mapper 052          =
 ========================
 
 Example Game:
 --------------------------
 Mario 7-in-1
 
 
 Notes:
 ---------------------------
 
 Yet another MMC3 multicart.  For info on MMC3, see mapper 004.
 
 
 Registers:
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   $6000-7FFF:  [.MHL SBPP]  Multicart reg
        P = PRG Block (bits 0,1)
        B = CHR+PRG Block Select bit (PRG bit 2, CHR bit 1)
        S = PRG Block size (0=512k   1=256k)
        L = CHR Block low bit (bit 0)
        H = CHR Block high bit (bit 2)
        M = CHR Block size (0=256k   1=128k)
 
   $8000-FFFF:  Same as MMC3 for selected block
 
 
 $6000 can only be written to once ... and only if PRG-RAM is enabled and writable (see $A001).  Once $6000
 has been written to, $6000-7FFF maps to PRG-RAM
 
 
 
 PRG Setup:
 ---------------------------
 
    'S'    PRG-AND    PRG-OR
    ------------------------
     0       $1F    %BP0 0000
     1       $0F    %BPP 0000
 
  'B' and 'P' bits make a 3-bit value used as PRG-OR (left shift 4).  When 'S' is clear, the low bit of that
 value is forced to 0.
 
 PRG swapping behaves just like a normal MMC3 within this selected block
 
 
 CHR Setup:
 ---------------------------
 
    'M'    CHR-AND    CHR-OR
    ------------------------
     0       $FF    %HB 0000 0000
     1       $7F    %HB L000 0000
 
  'H', 'B' and 'L' bits make a 3-bit value used as CHR-OR (left shift 7).  When 'M' is clear, the low bit of
 that value is forced to 0.
 
 CHR swapping behaves just like a normal MMC3 within this selected block
 
 
 Powerup and Reset:
 ---------------------------
 
 $6000 set to 0 on reset and powerup.