Date   : Fri, 24 Jul 2009 19:33:22 +0200
From   : rick@... (Rick Murray)
Subject: Fw: Fwd: ITV Teletext to shut down in January

Philip Pemberton wrote:

>   (1)- Adding VBI data to an existing video signal. For this you need a 
> composite input and a sync separator. The LM1881 costs about ?3 and 
> needs three or four external parts. Simple!

Whoo - custom teletext subtitling! :-)


>   (2)- Creating your own video signal as well. Bit more complex, now you 
> need a framebuffer and a sync generator.

Why do you need a frame buffer? If we are interested in playing with
TELETEXT, surely the picture part is of less consequence? Yes, you could
have a nice rendered JPEG saying "Press [text] now", but it would likely
be easier for you to say that.

Instead of a frame buffer, just use a circuit to fake a blank picture -
so long as the timing is good, surely we can just spit out black level
for the picture 'content'? Or with a little bit of additional circuitry,
paste two vertical white bars on the screen for another retro moment -
remember the naff tuning pattern built into loads of early VCRs? :-)

> but Betamax might (just about) work.

Got one of those. Could do with a better working one, but they're kinda
thin on the ground.


> That's how I'd do it anyway :)

Okay, got some veroboard and warming up my soldering iron... but I have
a horrible feeling you have skipped over the complicated bit - namely
you said with two RAMs you could write one while displaying from the
other - how will we manage that - is there enough available bandwidth to
1MHz bus it? How much data are we talking here anyway?


Best wishes,

Rick.

-- 
Rick Murray, irregular internet access at local library.
BBC B: DNFS, 2 x 5.25" floppies, EPROM prog, Acorn TTX
E01S FileStore, A3000/A5000/RiscPC/various PCs/blahblah...