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Technical information about DS90CF384

Other Parts Discussed in Thread: DS90CF384

Hello,


I need help about the DS90CF384 and video size.

Actually we use this part to receive LVDS signals from a PC board SBC84833 (Axiomtek) in 800x600 24 bits. All works fine. Now we have to change the PC board (SBC84833 is obsolete) to a CAPA831 (Axiomtek too). 800x600 24 bits is not avalaible with the CAPA831, so we have to use 1024x768 in 24bits and that don't work : the DS90CF384 don't reproduce the VS and HS sync. The reproduced Pixel clock is at 55Mhz (not 65 Mhz), is it possible that this frequency is not good in 1024x768  and the DS90CF384 don't work fine ?

I precise that with the SBC84833, that works in 1024x768 24 bits, but the pixel clock is at 65Mhz.

Best Regards,


Samuel

  • Hi Samuel,

    From a rough estimate, we can say that with the old SBC84833 outputting 800 x 600 with a presumed frame rate of 60 Hz, the clock is approximately 800 x 600 x 60 fps x 1.2 (approx. blanking interval) = 34.56 MHz. This is within the supported clock rate.

    Likewise, with the CAPA831, outputting 1024 x 768 with presumed frame rate of 60 Hz seems fine. The clock is approximately 1024 x 768 x 60 fps x 1.2 (approx. blanking interval) = 56.623 MHz, also within the supported clock rate. This may be why you are seeing the pixel clock produce around a 55 MHz signal. From an overview standpoint, I believe this resolution should work fine with the DS90CF384.

    Can you share a few things with us to help us understand what is going on?

    - Do you have a panel specification to indicate how big the blanking interval is? Is the frame rate going to be 60 Hz? That will allow us to get an accurate estimate of what pixel clock should be that is coming from the CAPA831.

    - If possible, can you have the old SBC84833 output 1024 x 768 and take a scopeshot of the output pixel clock and HSync, VSync from the DS90CF384? Then, if you can provide a scopeshot of the same signals but with the new CAPA831 providing signals to the DS90CF384, we can compare the signals from the different sources.

    - What pixel clock frequency is the CAPA831 providing?

    - Any schematics you can share?

    Thanks,

    Michael

  • Hi,

    With SBC84833, in 800x600 60Hz, pixel clock is at 40Mhz, not 34.56Mhz. That's work.

    With SBC84833, in 1024x768 60Hz, pixel clock is at 65Mhz, not 56.623Mhz. That's work.

    With CAPA831, in 1024x768 60Hz, pixel clock is at 56Mhz. That don't work. Since yesterday, a new bios of CAPA831 to use the LVDS 1024x768 in 60Hz with pixel clock at 65Mhz have be done by the PC board manufacturer, without results...So I don't think it's a frequency issue.

    I will try to give the informations.


    The frame rate is 60Hz but I don't know the blanking interval. In attachment you can find scopeshots for SBC84833 and CAPA831 for the CLK, EN, HS and VS. It's possible that the signals are not very properly, especially the clock but it's du to my measurement.

    The pixel clock of the CAPA831 is around 56MHz.


    If needed, I will upload, the schematics of the DS90CF384 at the next post.

    Otherwise, we will try another PC board reference, the CAPA111 to see if the problem persist. It's strange...SBC84833 and CAPA831 are from the same manufacturer Axiomtek. It seems that HS and VS are not transmitt through the LVDS link with the CAPA831...

    Thank you for your expert assessment, I will come back to you when we tested the CAPA111 or if you are any suggestions.

    Best Regards,