
========================
=  Mapper 091          =
========================

Example Games:
--------------------------
Street Fighter III
Super Mario & Sonic 2


Notes:
---------------------------
Regs exist at $6000-7FFF, so this mapper has no SRAM.


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

Range,Mask:   $6000-7FFF, $7003

  $6000-6003:  CHR Regs
  $7000-7001:  [.... PPPP]  PRG Regs

  $7002 [.... ....]  IRQ Stop
  $7003 [.... ....]  IRQ Start



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

      $0000   $0400   $0800   $0C00   $1000   $1400   $1800   $1C00 
    +---------------+---------------+---------------+---------------+
    |     $6000     |     $6001     |     $6002     |     $6003     |
    +---------------+---------------+---------------+---------------+

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

      $8000   $A000   $C000   $E000  
    +-------+-------+-------+-------+
    | $7000 | $7001 | { -2} | { -1} |
    +-------+-------+-------+-------+


IRQs:
---------------------------

IRQs on this mapper seem to behave exactly like MMC3 -- except it's fixed so that it will only fire after 8
scanlines.  This is easily emulatable by using MMC3 logic.

Write to $7002/$7003 can translate directly to write(s) to the following MMC3 registers:

on $7002 write:
   a) write to $E000

on $7003 write:
   a) write $07 to $C000
   b) write to $C001
   c) write to $E001


For details on MMC3 IRQ operation, see mapper 004