The NEC 7220 is rather complex, and several features are missing in the current code (RMW cycles for example).
I now have a playable version of SCRAM... only the diagnostic disk is unimpressed. There is certainly a long way to go.
BTW, i found a good article by Guido Dampf (from 1986, in German) about the inner workings of this chip, with Turbo Pascal source. An abridged version in English is somewhere, too.
Crazyc, do you happen to know it?I plan to submit my current status soon and hope for improvements by others. As stated above, Pacman, Doodle and Scram offer fine test cases (apart from the GDC diagnostic disk).