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old graphical interface to screen connection

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Hello there,

I am on the project to rebuild a 'high' resolution color graphical interface (description in several parts into Elektor n° 87 to 94) for my Junior Computer.

These boards provide the video signal at TTL level (R+G+B+CSync).

The pixel clock is 12 Mhz, usually vga monitor dont handle so low frequency....

What is the best and simplest solution for connecting that to a lcd tv (scart ?) or to a vga monitor ? If I can find something ready to use...

Thanks for help.

I dug up the first page of the article in question, and it says 64 us per line and a 50 Hz frame rate.  That's 15.625KHz line frequency, so its RGB component video using PAL/SECAM sync timings. 

It should connect direct to any European TV with a SCART connector.  If you want to use it with a SVGA monitor you'd need to run its output through a scanrate converter.

But then I have to made level converters...
Scart is not for TTL level.


--- Quote from: Wawavoun on May 11, 2022, 08:33:12 am ---But then I have to made level converters...
Scart is not for TTL level.

--- End quote ---

Accepts SCART direct input and outputs RGB signal

there is also a dedicated NTSC version of this chip

I have a half dozen


For analog video, peak white or single R,G or B component should be +1.0V, black +0.3V, and if it has sync (sync on green or composite video) 0V for the sync pulses.

Usually, TTL  RGB => SCART RGB was a simple series resistor to form an attenuator with the 75 ohm SCART RGB input impedance, The resistor was typically somewhere between 180 to 330 ohms depending on how high the TTL RGB output swung under load. 

If the black level overdrive (dropping to 0V rather than 0.3V) is a problem, or if you need to add in an intensity signal, it gets more complex and  you'll probably have to build a proper level converter.   


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