INES Mapper 076: Difference between revisions

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(Created page with "Category:iNES Mappers Here are Disch's original notes: ======================== = Mapper 076 = ======================== Example Games: ---------…")
 
m (Updated broken bootgod link to redirect to NESCartDB page for Megami Tensei: Digital Devil Story.)
 
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[[Category:iNES Mappers]]
[[Category:iNES Mappers|076]][[Category:MMC3-like mappers|076]][[Category:in NesCartDB|076]]
  Here are Disch's original notes:
[[iNES Mapper 076]] represents '''NAMCOT-3446''', a board used only for the game [https://nescartdb.com/profile/view/2308/megami-tensei-digital-devil-story Megami Tensei: Digital Devil Story].
  ========================
 
  =  Mapper 076         =
It rewires the [[iNES Mapper 206|Namcot 108]] mapper IC to be able to address 128 KiB of CHR, in exchange for coarser CHR banking.
  ========================
 
 
  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.
    
    
The PCB also has a [[7432]] which allows the use of a 28-pin CHR-ROM.
    
    
   Registers:
   Registers:
   ---------------------------
   ---------------------------
  Mask: $E001
    
    
  Range,Mask:  $8000-FFFF, $E001
     $8000:  [.... .AAA]
 
 
     $8000:  [.P.. .AAA]
      P = PRG register select (see PRG setup)
       A = Address for use with $8001
       A = Address for use with $8001
    
    
 
     $8001:  [..DD DDDD]    Data port:
     $8001:  [DDDD DDDD]    Data port:
         R:2 ->  CHR reg 0  (2k @ $0000)
         R:2 ->  CHR reg 0  (2k @ $0000)
         R:3 ->  CHR reg 1  (2k @ $0800)
         R:3 ->  CHR reg 1  (2k @ $0800)
         R:4 ->  CHR reg 2  (2k @ $1000)
         R:4 ->  CHR reg 2  (2k @ $1000)
         R:5 ->  CHR reg 3  (2k @ $1800)
         R:5 ->  CHR reg 3  (2k @ $1800)
         R:6 ->  PRG reg 0 or 2 (depending on 'P' bit in $8000)
         R:6 ->  PRG reg 0  (8k @ $8000)
         R:7 ->  PRG reg 1
         R:7 ->  PRG reg 1 (8k @ $a000)
 
 
    $A000:  [.... ...M]
      Mirroring:  0=Vert
                  1=Horz
    
    
   CHR Setup:
   CHR Setup:
   ---------------------------
   ---------------------------
 
         $0000  $0400  $0800  $0C00  $1000  $1400  $1800  $1C00  
         $0000  $0400  $0800  $0C00  $1000  $1400  $1800  $1C00  
       +---------------+---------------+---------------+---------------+
       +---------------+---------------+---------------+---------------+
       |      R:2      |      R:3      |      R:4      |      R:5      |
       |      R:2      |      R:3      |      R:4      |      R:5      |
       +---------------+---------------+---------------+---------------+
       +---------------+---------------+---------------+---------------+
 
    
    
   PRG Setup:
   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   
         $8000  $A000  $C000  $E000   
       +-------+-------+-------+-------+
       +-------+-------+-------+-------+
       |  R:6a |  R:7  | R:6b | { -1} |
       |  R:6  |  R:7  | { -2} | { -1} |
       +-------+-------+-------+-------+
       +-------+-------+-------+-------+
 
 
 
  Powerup:
  ---------------------------
 
  R:6b seems to be reset to $FE on powerup.  The game does rely on this.

Latest revision as of 01:27, 14 September 2023

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} |
     +-------+-------+-------+-------+
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