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We need your help with AM1810 pin problems!

Guotao Zhang
Intellectual 705 points
Other Parts Discussed in Thread: AM1810, OMAP-L138

Hi Professionals! My team met a problem again. On our AM1810 developer board, we are going to  provide digital clock signal excitaion for FPGA chip by digital output of pin of CLKOUT/UHPI_HDS2/PRU1_R30[13]/GP6[14]. After our configuration on AM1810 board, we used oscillometer AC block to test output of this pin and result is a 24MHz triangle wave with an amplitude of ~2V. But we are wondering: should the waveform have been square wave, instead of triangle wave? Actually we hope it is square wave. Please help us analyse it. Thank you very much. 

  • 0
    TI__Expert 4760 points

    Hi Guotao,

    The CLKOUT is a perfect square wave output .Please check your oscilloscope probe configuration you’re mentioning about the AC block to test the output please check that one ,a simple passive  RC integrator circuit can change the Square wave into triangular wave.

    More over the CLKOUT on AM1810 have a VPP of 1.8V or 3.3V depending on how the power group C is sourced.

    The CLKOUT when initially spec'd was made available more from a debugging aid standpoint. It should be fine to be able to use the CLKOUT as a clock source. While the IO buffer on this pin is similar to EMA_CLK (runs upto 100+ MHz) , it is likely that the signal quality of the signal will start to degrade significantly at higher clock speed. So it would be best to do an IBIS analysis to see what is the max speed you can get for the load conditions you specified.

    Regards

    Antony

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  • 0 in reply to Antony Samsunil
    Intellectual 705 points

    Hi Antony! Thank you for your quick response. We are trying to reset value of PLLC0 OBSCLK Select Register (OCSEL). But we cannot find the corresponding function interface for this register in OMAP-L138_FlashAndBootUtils_2_40, or u-boot-2009.11-psp03.30.00.02 or linux-2.6.33-rt29-psp03.30.00.02. 

     

    So could you please tell us where we are able to find it? Thank you very much. 

  • 0 in reply to Guotao Zhang
    TI__Expert 4760 points

    Hi Guatao,

    Please find the attached gel script for OBSCLK control.

    Regards7002.OMAPL1x_debug.gel

    Antony

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  • 0 in reply to Antony Samsunil
    Intellectual 705 points

    Hi Antony! Thank you very much. As you said, oscilloscope probe configuration should be paid additional attention. Today we tested the waveform at clock frequency of 2M, 10M and 96M and for 2M and 10M, perfect square wave. But for 96M, it is sinewave and we think it was caused by the signal quality degradation as you mentioned or we guess it's our osilloscope's measurement range constraint. We haven't tested at 24M (default value) yet, but we deduce that there will be also perfect square wave at 24M frequency. 

    Thanks a lot again.

    Best regards!

    Guotao