INES Mapper 230

 Here are Disch's original notes:  
 ========================
 =  Mapper 230          =
 ========================
 
 Example Game:
 --------------------------
 22-in-1
 
 
 Reset Driven:
 ---------------------------
 The mapper has 2 main modes:  Contra mode, and multicart mode.  Performing a Soft Reset switches between
 them.
 
 
 Notes:
 ---------------------------
 
 This multicart has an odd PRG size (not power of 2).  This is because there are 2 PRG chips.
 The first is 128k and contains Contra, the other is 512k and contains the multicart.
 
 A soft reset changes which chip is used as well as other stuff relating to the mode
 
 
 Registers:
 ---------------------------
 
 
  Contra Mode $8000-FFFF:     [.... .PPP]
 
  Multicart Mode $8000-FFFF:  [.MOP PPPP]
 
     M = Mirroring (0=Horz, 1=Vert)
     O = PRG Mode
     P = PRG Page
 
 Note:
   Mirroring is always Vert in Contra Mode.
 
 
 
 PRG Setup:
 ---------------------------
 
                 $8000   $A000   $C000   $E000  
               +---------------+---------------+
 Contra Mode:  |     $8000     |     { 7 }     |  <---  use chip 0
               +-------------------------------+
 Multi Mode 0: |             <Reg>             |  <---  use chip 1
               +-------------------------------+
 Multi Mode 1: |      Reg      |      Reg      |  <---  use chip 1
               +---------------+---------------+
 
 
 chip 0 = 128k PRG  (offset 0x00010-0x2000F)
 chip 1 = 512k PRG  (offset 0x20010-0xA000F)