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SN65DP141: Behaviour when DisplayPort redriver is powered down to the downstream device

Jay Aura
Prodigy 10 points
Part Number: SN65DP141

Hi,

I would like to understand the behaviour of the SN65DP141 redriver when the PWR pin is asserted. Datasheet says the chip goes to a low power mode and I2C lines are reset.

My question is, what exactly does a downstream DP device connected to the output end of redriver see. While the chip if operating normally, is asserting PWR enough to indicate a hot unplug? Similarly, would powering the chip back on by de asserting PWR trigger the same effect as a hot plug ?

  • 0
    TI__Guru**** 175781 points

    Hi,

    If DP141 is in Power Down mode, then the downstream DP device will notice the loss of signal at its input and may notify the DP source this change of event by attempting a HPD interrupt. The HPD interrupt is when the downstream DP device generates a low-going HPD pulse of 0.5ms → 1ms in duration. But it is not the same as the HPD unplug/plug. When source detecting this “IRQ HPD pulse”, the source device must read the downstream device link/sink status field of the DPCD registers and take corrective action through the AUX bus. 

    Thanks

    David

  • 0 in reply to David (ASIC) Liu
    Prodigy 10 points

    Thanks for the quick and detailed response David! I intend to Hi-Z Aux lines and HPD pin separately, so upstream device will not get the HPD IRQ. Whats my best shot to make the downstream device do a HPD Detect pulse (at least 2ms wide) ?

  • 0 in reply to Jay Aura
    TI__Guru**** 175781 points

    Hi,

    I am not sure if I fully understand your question. The AUX and HPD are implemented outside the DP141 as shown in this simplified block diagram.

    Are you trying to Hi-Z the AUX and HPD pin on the source side? If this is the case, then DisplayPort will not work since both AUX and HPD are required.

    Thanks

    David

  • 0 in reply to David (ASIC) Liu
    Prodigy 10 points

    Sorry, let me clarify. I will use another controller to assert PWR and Hi-Z the aux and hpd when not needed. During normal operation, aux and hpd shall not be interrupted. I would have additional circuit to take care of that.

  • 0 in reply to Jay Aura
    TI__Guru**** 175781 points

    Hi,

    Can you share a block diagram of what you are trying to do? I want to make sure there is no misunderstanding here.

    Thanks

    David

  • 0 in reply to David (ASIC) Liu
    Prodigy 10 points

    I hope this clarifies what I'm trying to do. PWR that goes to DP141 and the control signal that goes to the analog circuit which switches HPD&Aux shall be triggered at the same time when i want the downstream device to be disconnected.

  • +1 in reply to Jay Aura
    TI__Guru**** 175781 points

    Hi,

    If you Hi-Z the AUX and HPD when not needed, it will be seen by the source and the sink as a disconnect or unplug event. In this case, it really doesn't matter whether PWR is being driven high or low.

    But back to the normal operation, you want to make sure the DP141 is out of the power down mode first before enabling the HPD and AUX.

    Thanks

    David