help about the mapper of street fighter 2

[woshizyt]

   I am looking for some information about the mapper of street fighter 2,below is some description.

Street Fighter II:
  - address space banks 40-7F switchable by writing to 1FF0-1FF3
    1FF0 - select rom banks 40-7F
    1FF1 - select rom banks 80-BF
    1FF2 - select rom banks C0-FF
    1FF3 - select rom banks 100-13F

below writed by Bonknuts ,thanks!
 " The SF2 mapper is dead simple. If you're familiar with Famicom, it's not unlike unrom and other such simple mappers in it's simplicity. The game uses the whole lower 8mbit external address range (typical hucard range). The bottom 4mbit range is fixed to the first 4mbit of the rom, the upper 4mbit of the 8mbit hucard range is used for swapping in 512k(4mbit) banks. So it's a 4Mbit+16Mbit format. Writing any value to 'external' address range of $1ff0 to 1ff3 selects which 4Mbit segment of the 16Mbit segment gets mapped into the upper 4Mbit hucard area. So $1ff0 = bank 4Mbit #0, $1ff1 = bank 4Mbit #1, etc."

I want to make the mapper be a really TTL logic circuit,and below pic is the work Block diagram Based on my understanding.

anyone could give me some suggestion?I am very grateful for your answer.