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AM3874: HDMI issues if monitor has dynamic impedance

pathfinder
Genius 12790 points
Part Number: AM3874


Hello,

Are there any known issues with HDMI/DVI driving various monitors that present different impedance?

If monitor momentarily Ground TMDS signals, can this cause device damage?

Thanks,
Marc

  • 0
    TI__Guru**** 170625 points

    Marc,

    pathfinder said:
    Are there any known issues with HDMI/DVI driving various monitors that present different impedance?

    I am not aware of such known issue. AM387x HDMI is 1.3a standard compatible and should work fine with every monitor that is compatible with this 1.3a standard.

    pathfinder said:
    If monitor momentarily Ground TMDS signals, can this cause device damage?

    You should check the 1.3a HDMI standard. If this standard does not allow "monitor momentarily Ground TMDS signals", then probably AM387x device will be damaged.

    Regards,
    Pavel

  • 0 in reply to Pavel Botev
    TI__Genius 12790 points

    Pavel,

    Can you verify that HDMI controller and TMDS control can be disabled or 'turned off'?  What actually happens to the TMDS lines if it disabled?

    According to Technical Reference Manual for AM3874, here are some registers that relate to TMDS:

    • In Table 13-244. TMDS Control Register 2 (TMDS_CNTL2) Field Descriptions, Bit 5  should be 0 (Output drivers of TMDS outputs are switched off), and bit 4 should be 0 (Bus termination is switched off).
    • In Table 13-245. TMDS Control Register 3 (TMDS_CNTL3) Field Descriptions, bit 0 should be 0 (PHY will be power down).

    I assume AM3874 can disable TMDS driver if set those bits in the registers to 0. Please help us to verify.

    Thanks.

    Marc

  • 0 in reply to pathfinder
    TI__Guru**** 170625 points
    Marc,

    Yes, you can turn off HDMI output.

    With linux driver, you can turn OFF streaming / stop display, using TI81XXHDMI_STOP ioctl. Check the below wiki for more info:

    processors.wiki.ti.com/.../TI81XX_PSP_HDMI_Driver_User_Guide

    Regarding TMDS registers, refer to the below e2e threads:

    e2e.ti.com/.../190101
    e2e.ti.com/.../518499

    Regards,
    Pavel