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DS90UH941AS-Q1: Display on the LCD screen is jumping up and down. Which parameters might be wrong?

Part Number: DS90UH941AS-Q1
Other Parts Discussed in Thread: DS90UB948-Q1,

Hi:

      I'm using DS90UH941AS-Q1 and ds90ub948-q1. the connection is :

 

     SOC ---->  DS90UH941AS ---> FPDLINK --->  ds90ub948 --> lvds ---> LCD

     I'm also using an external clock source for DS90UH941AS . which is set to 133MHz. Both 941 and 948 are Forced Dual FPD-Link III mode.

     the resolution of the LCD is 1920*1080@60fps DE mode. The parameter of the porch setting or the clock polarity setting is done on the SOC side.

    The problem is this:

    The screen display is generally ok. EXCEPT that the entire display is moving up or down every second. Kind of like jumping up and down.

    When the entire display is moving up. it will move up like 10-20 pixels vertically.

   I also tried the pattern mode test for both 941 and 948. They look ok.

    Tried to change the hsync/vsync/pixel clock polarity setting on the SOC side. But it doesn't seem to be related.

  The voltage of LOCK pin of 948 is checked and it is constantly high.

   Any idea what might be the cause?

PS: when the boot animation is being displayed. the animation jumps both up/down and left/right.

after the android launcher is ready. it start to jump only up/down

  

  • Solved.

    the external clock has the spread spectrum feature turned on for EMC purpose.

    since the DE mode panel strictly depend on pixel clock for syncing. vsync and hsync is not applied.

    thus the pixel clock has to be very accurate.

    turning off the spread spectrum feature solved the problem