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DS90UB948-Q1: Timing of GPIO and LVDS output to TFT

Jade Lan
Intellectual 1110 points

Part Number: DS90UB948-Q1

Hi team,

The customer is using GPIO8 of 948 as the standby signal for the TFT and their power-on process requires pulling up the standby signal. The following issues need to be confirmed.

1. When testing the output of GPIO8, the customer found that GPIO8 outputs a PWM wave for a short period of time after power-on. Is this phenomenon normal?

The output of GPIO8 when connected to the screen is shown in blue.

image.png

The output of GPIO8 when the screen is not connected is as follows.

image.png

2. If the above phenomenon is normal, then the customer needs GPIO8 of the 948 to output a high level to the TFT first, and then output the LVDS video signal; otherwise, the screen may be at risk of flickering. Is it possible to configure the timing of GPIO and LVDS outputs to the TFT via software?

BR,

Jade

  • 0
    TI__Expert 5193 points

    Hi Ragav,

    The replies are as follows:

    Ragav Subramanian said:
    Can you confirm if the behavior occurs when the TFT is powered down?

    The first waveform was measured with 948 connected to the TFT and the TFT powered on. The second waveform was measured with 948 not connected to the TFT.

    Ragav Subramanian said:

    Are you setting GPIO8=High via software following the register write below:

    Yes.

    I would appreciate your confirmation on the following two questions.

    • Is it normal for a PWM waveform to appear on GPIO8 after powering on 948? Hope you can test it and then provide your conclusions.
    • Is it possible to control the timing of LVDS and GPIO signals from 948 to the screen via software? The customer wants to use register 0x2 to make LVDS video stream is output to the TFT after GPIO8 of the 948 outputs a high level for 300ms.

    Looking forward to your reply, thank you.

    BR,

    Jade