
  regs:
  0x5000 - 32k bank data   %bxxxxaaaa
    aaaa - bank number.
  0x5100 - 512k EPROM area %bxxxxxxxb
       b - 0 - first 512Kb area,
           1 - second 512Kb area.
  0x5200 - unknown
  0x5300 - unknown
  

  At power ON reg 0x5000 point to last bank (0xF), but 0x5100 regs is
  zero, so that point to first 512Kb area...