PZ wrote:
Bryan: I think Ed wants to put an inverted 68pin PLCC socket on top of
the FPI/CYA chip and tap the ABUS and DBUS directly that way; thus his
need to generate his own refresh signals. Neither IC is socketed on
ROM 01s or 03's, so it could be an easy universal implementation if the
board can be made small enough.
Ed: I'd take a look at an old Apple II+ Schematic. I've never peeked
at the refresh circuitry there directly, but that would probably give
you the best implementation using Apple II timing signals. It should
be all there, you just need to scale things a bit.
There is no special refresh logic in an 8-bit Apple II.
Refresh is simply a side effect of the address progression of
the video scanner as it "refreshes" the screen. ;-)
That's why the video buffer addresses are nonlinear.