INES Mapper 245

Mapper 245 is an MMC3 clone uses bit 2 of CHR Register 0 to select which 512KB bank of PRG ROM is seen. This increases the maximum PRG size up to 1024K. CHR RAM is not bankable (equivalent to the bank numbers being fixed at 0, 2, 4, 5, 6, and 7), but the top bit of $8000 will still switch the left and right pattern tables.

 Here are Disch's original notes:  
 ========================
 =  Mapper 245          =
 ========================
 
 
 Example Games:
 --------------------------
 Yong Zhe Dou e Long - Dragon Quest VII (As)
 
 
 Notes:
 ---------------------------
 Another ?Chinese? MMC3 clone.  Very similar to your typical MMC3.  For MMC3 info, see mapper 004.
 
 Register layout is identical to a typical MMC3.
 
 
 
 CHR Setup:
 ---------------------------
 
 CHR-RAM is not swappable.  When there is no CHR-ROM present, 8k CHR-RAM is fixed.  However the CHR Mode bit
 ($8000.7) can still "flip" the left/right pattern tables.
 
 Example:
 
                     $0000   $0400   $0800   $0C00   $1000   $1400   $1800   $1C00 
                   +-------------------------------+-------------------------------+
 CHR-RAM, Mode 0:  |             { 0 }             |             { 1 }             |
                   +-------------------------------+-------------------------------+
 CHR-RAM, Mode 1:  |             { 1 }             |             { 0 }             |
                   +---------------------------------------------------------------+
 CHR-ROM:          |                          Typical MMC3                         |
                   +---------------------------------------------------------------+
 
 
 PRG Setup:
 ---------------------------
 
 PRG Setup is the same as a normal MMC3, although there's a PRG-AND of $3F, and games select a 512k Block with
 bit 1 of R:0.  Pretty simple really:
 
    R:0:  [.... ..P.]
 
   'P'    PRG-AND    PRG-OR
  --------------------------
    0       $3F        $00
    1       $3F        $40
 
 
 R:0 remains the normal MMC3 CHR reg, as well.  Although the game that uses it as a PRG block selector ("DQ7")
 uses CHR-RAM, so it is normally ignored.