Extensions:
1) Mapper allow to use up to 15 Mbyte of memory
2) Write acces to ROM memory. ROM memory can be used as RAM
3) First bank can be switched like any other bank
4) Oboard Led control

registers:


0xA130F0 [PXWL.... ...RRRRR] write only
  P is a protection bit. Bit P always should be set for any manipulations with reg 0xA130F0 (0=access to register is deny, 1=new value can be loaded)
  X 32x mode. Should be set in case if game use 32x
  W ROM memory write protect (0=not writable, 1=writable)
  L LED (0=off, 1=on)
  R 512Kbyte bank
 

0xA130F2-0xA130FE [........ ...RRRRR] write only
   R 512Kbyte bank

Mapper will be activated in case if ROM header contains "SEGA SSF" string, instead of standard "SEGA GENESIS" string.

Banks 30-31 used by OS, not recommended to touch them, otherwise OS may not boot after reset, in this case OS will start only after cold start.

Bank 28 can be used for saves. First 32Kbyte of this bank will be copied on SD