> I believe the 1 MHz video system you might be referring to actually had a
> so
> called "VIC" which handled the video part. The only thing the processor
> did
> was share the memory with it occasionally.



My OSI-C1P had no such chip.



The only system old system that I
> recall that did video stuff on the main processor used a Z80A at 4.77 MHz
> and had a special logic chip that aided in generating the (black and
> white)
> video output. It had a "FAST" option, that disabled the video processing,
> causing the system to run 5x faster than normal, but without showing
> anything, obviously.


Sounds like a ZX-81



Don Lancaster's TV Typewriter books have the basics.
Overlaying is a bit more complicated, as you have to sync up with the
incoming video, but not THAT much worse.
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