INES Mapper 089

This mapper is used by Tenka no Goikenban: Mito Koumon (J). This game uses the Sunsoft-2 chip, but it works differently than Mapper 093 (the board must be wired differently?)

Here is the documentation in disch's original style:

 Registers:
 --------------------------
   $8000-FFFF:  [CPPP MCCC]
     C = Select 8k CHR @ $0000
     P = Select 16k PRG @ $8000
     M = Mirroring:
       0 = 1ScA
       1 = 1ScB
 
 
 PRG Setup:
 --------------------------
 
       $8000   $A000   $C000   $E000  
     +---------------+---------------+
     |     $8000     |     { -1}     |
     +---------------+---------------+

 Notes:
 ---------------------------
 I do not know whether or not this mapper suffers from bus conflicts.  Use caution!