So real hardware does pulse the bit.

Yes but the 0xaa is placed there when the bit goes up again, not before.
Their detection routine is broken, but works if the last command (which could
be from some other game/demo, or the default value from bootup) did
return with 0xaa.

anyway, there's a patch for Mental Surgery on my site, so now it works even with the broken method.

Damnit, my timebase was wrong... the Aztech takes only 50 microseconds until ready. I forgot in mode 3 the system timer counts in steps of two...

@wd: So the Adlib timers are not wrong.

Ok, thanks for checking that.