
========================
=  Mapper 228          =
========================


Example Games:
--------------------------
Action 52
Cheetah Men II


Notes:
---------------------------
Cheetah Men II is infamous for how freaking terrible it is.  Action 52 is none better.  These games are SO
bad, it's hilarious.

Action 52's PRG size is weird (not a power of 2 value).  This is because there are 3 seperate 512k PRG chips.
PRG Setup section will cover details.


Powerup and Reset:
---------------------------
Apparently the games expect $00 to be written to $8000 on powerup/reset.


Registers:
---------------------------

  $4020-4023:  [.... RRRR]  RAM  (readable/writable)
                (16 bits of RAM -- 4 bits in each of the 4 regs)
  $4024-5FFF:    mirrors $4020-4023

  $8000-FFFF:    [.... ..CC]   Low 2 bits of CHR
               A~[..MH HPPP PPO. CCCC]

    M = Mirroring (0=Vert, 1=Horz)
    H = PRG Chip Select
    P = PRG Page Select
    O = PRG Mode
    C = High 4 bits of CHR

CHR Setup:
---------------------------

      $0000   $0400   $0800   $0C00   $1000   $1400   $1800   $1C00 
    +---------------------------------------------------------------+
    |                             $8000                             |
    +---------------------------------------------------------------+


PRG Setup:
---------------------------

'H' bits select the PRG chip.  Each chip is 512k in size.  Chip 2 does not exist, and when selected, will
result in open bus.  The Action 52 .nes ROM file contains chips 0, 1, and 3:

chip 0:  offset 0x000010
chip 1:  offset 0x080010
chip 2:  -- non existant --
chip 3:  offset 0x100010

'P' selects the PRG page on the currently selected chip.

               $8000   $A000   $C000   $E000  
             +-------------------------------+
PRG Mode 0:  |            <$8000>            |
             +-------------------------------+
PRG Mode 1:  |     $8000     |     $8000     |
             +---------------+---------------+

