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LMH1980: Display observed on VGA monitor getting blanked due to un expected HSYNC Pulses

Tendulkar S
Prodigy 30 points
Part Number: LMH1980

Dear sir,
 
            I am using LMH1980 as a SYNC separator to separate the HSYNC , VSYNC from green video of VGA(composite SYNC has been inserted in green video of VGA).But un expected HSYNC pulses are observed at output of LMH1980.
Due to this , no video is obsered on Display (i.e display is completely blank).
 
I have attached the design description and probed scope images with this mail.Kindly check once and help us to solve the problem.
 
Note : Display configuration -- 1024 X 768 @ Refresh rate 60Hz (Verticle sync polarity : Negative, Horizontal SYNC polarity : Negative)
 
Tendulkar S
Hardware Design and DevelopmentLMH1980_SYNC_SEP_Improper_HSYNC.pdf

  • 0
    TI__Mastermind 32575 points

    The LMH1980 was tested formats using Unigraf VTG-3030 test pattern generator for PC graphics formats using Serrated or (H+V) composite mode.  Here's the link to the test pattern generator datasheet: www.dssrl.com/.../vtg3030.pdf

    Your design generates composite syncs using (H exor V) scheme, so the LMH1980 may not support that.  I recommend you try generating composite sync using Serrated or H+V composite sync mode.

    Regards,
    Alan

  • 0 in reply to Alan O
    Prodigy 30 points
    Thank you for reply.
    But it VTG-3030 ,VTG-3016 it is given that Composite modes
    H+V, H exor V , serrated and my design is same like composite SYNC generated from H exor V.

    Do you have and design scheme or schematics to generate the -- PC graphics formats using Serrated or (H+V) composite mode design.

    Regards
    Tendulkar S
  • 0 in reply to Tendulkar S
    TI__Mastermind 32575 points
    We did not test H exor V with VTG-3030. I don't know how to generate the serrated composite sync. To generate H+V, I think it is just the logical OR-ing of the H and V sync signals.

    Regards,
    Alan