See the Wiki for more details 
(http://www.awce.com/classroom/course/view.php?id=11).

=== Changes since the DDJ Version
Interrupts
FDEBUG unit

=== Changes sine the "C" Version
External RAM memory on the Spartan board is used (1MB or 256Kwords)
ALU is shared to save die area
PC Bus is improved
25MHz operation (12.5MIPS)
Flags read out slightly differently (one copy high and one copy low as before)

