piclist 2000\11\30\075320a >
Thread: SCENIX VIDEO VIRTUAL PERIPHERAL Design Challenge and Contest
picon face BY : Bob Ammerman email (remove spam text)

> While we are on the "we alone have ..." thought, look at the Clive "I can
> magic" Sinclair ZX80 which used an ancient and venerable (and venerated?)
> Z80 plus a shift register to work video magic. It also managed to pretend
> be a "full" computer during the flyback period. The CISC set-and-forget
> block move instruction has it's place :-).

Correct me if I am wrong, but...

I believe the ZX80 did _not_ use a block move instruction to do the video.
Instead, it set a special flag that indicated that it was about to
_execute_(!) video. When this flag was set the opcodes being fetched from
RAM were routed to the screen. Of course this would confuse the processor
something awful (or else really restrict what could be displayed). So, the
hardware would 'jam' a no-op onto the processor's data bus when the video
flag was set, regardless of what instruction was fetched from memory.

In other words: the program counter of the Z80 became the video refresh
address register.

> I'm sure the Scenix would be hard to beat in this application using a true
> single chip solution but it does wilt rather on other tasks in the face of
> some of the competition.

Sure would be nice to have a built in USART to shift out the dots. That is
how my PIC18C manages to get 432 H x 240 V pixels on the screen, including
animated graphics.

Bob Ammerman
RAm Systems
(contract development of high performance, high function, low-level

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<004301c05acb$a4dece20$f5e8c540@sciencekit.com> 7bit

See also: www.piclist.com/techref/ubicom/lib/io/index.htm?key=video
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Subject (change) SCENIX VIDEO VIRTUAL PERIPHERAL Design Challenge and Contest

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