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i think what ur looking for is a video overlay circuit.
I think they usually work by counting the horizontal and vertical sync of the video signal and when pixel matches then it modifies the RGB signals.
I don't know exactly how uPD6451 works, but i would guess that you can tie the hsync and vsync signals together and hardware OR the RGB bits from from uPD6451 and the live video signal. Of course this assumes that the resolution for both is the same (which is prolly not true). Oh well, i could just be talking out of my ass here...
"Mixing" output signal from the µPD6451 with "live" video is not difficult, if you go for white characters on top of everything ..
Program it for WHITE colour and signal will be available at RGB pins and Vblk ..
Of course, you need to extract V and H from the video signal, and that can be done with something like GS4881, or similar ..
If, however, characters have to be displayed in colours, that is a different story, and you will need to employ some sort of video processor with RGB inputs ..
Hi IanP,
At this stage I want to display something and white character color is OK.
I use LM1881 as sync separator.
Can you suggest mixing circuit?
Thanks in advance!
From input/output point of view this circuit is "transparent" and has hardly any influence on the video signal, except for adding some white dots here and there ..
If the value of the resistor between input and output is 0Ω, this video imposer should maitain all parameters of video signal and transmission line, 1Vpp and 75Ω, that is ..
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