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How to configure register for external Reference clock?

Luke Park
Prodigy 685 points
Part Number: SN65DSI85-Q1

Hi, Joel

At first, LVDS Pixel clock is sourced from MIPI D-PHY. Now Customer wants to test external Reference clock, 25MHz.

Display panel Pixel clock is 44.7MHz.

Case1)  Ref clock is from MIPI D-PHY and it is 44.7MHz.

Customer can configure clock through DSI Tuner tool. 

Case2) Ref clock is from external oscillator, 25MHz.

Customer wants to make 44.7MHz as same as before, but they don't how to configure.

Could you explain how to configure? Customer wants to know which register, which value?

  • 0
    TI__Mastermind 18655 points

    Hi Luke,

    Sorry for the delayed response. The clock source is selected by HS_CLK_SRC. If you select the external reference clock, it is multiplied by the factor in REFCLK_MULTIPLIER  to generate the  LVDS output clock. If the DSI channel A clock is selected, it is divided by the factor in DSI_CLK_DIVIDER to generate the LVDS output clock.Additionally,  you should configure  LVDS_CLK_RANGE and CH_DSI_CLK_RANGE to set the frequency range of the LVDS output clock and DSI Channel An input clock respectively.

    In the DSI Tuner, If Ref CLK is selected, you should enter the reference CLK frequency in the Ref CLK(MHz) field, then select the multiplier value (1-4) that satisfies the equation below: Ref CLK (MHz) x Multiplier value = LVDS CLK rate (pixel CLK for the LVDS panel). If DSI CLK is selected, enter the DSI channel A CLK frequency in the DSI Ch a CLK field then select the Divisor value (1-25).

    The closet output clock to 44.7Mhz with an external reference of 25Mhz will be 50Mhz when selected a multiplier of 2. Therefore, you should check if your panel supports this input clock (50Mhz) or use the LVDS input clock instead. 

    Regards 

  • 0 in reply to Joel Jimenez0
    TI__Prodigy 685 points

    Hi, Jeol

    Do you mean that

    External Reference of 25MHz can't match exactly same as 44.7MHz?

    The only way is to make closet output clock, 50MHz by multiplier of 2?

    What happen if panel can't support 50MHz? that mean panel should be changed to another one can support 50MHz?

  • 0 in reply to Luke Park
    TI__Mastermind 18655 points

    Hi Luke, 

    Yes, that is correct, by using an external clock of 25MHz, the closet clock that the device can output is 50MHz. 

    If your panel does not support 50Mhz, you can use the DSI clock to input the external clock or change the panel as you comment. 

    Regards