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SN65DP159: Image noise occurrence at low resolution (VGA) signal input

Masazumi Ishii
Genius 3945 points
Part Number: SN65DP159
Other Parts Discussed in Thread: TMDS171

Hello.

We are considering TPS65DP159.
We are currently verifying.

Flickering occurs on the screen when the input signal is low resolution.
In fact, it looks like multiple vertical line noise.

conditions
Input signals: 640 x 480 60 p, 720 x 480 60 p (HDCP OFF)
Occurrence environment: An input signal is generated using a specific signal generator and occurs. HDMI Rx / Tx Used SN65DP159 for each interface.
Symptoms occurred when used with Rx side Retimer.

SN65DP159 Setting
Rx: Retimer mode (Across full range 250 Mbps to 6 Gbps)
Tx: Retimer mode or (Across full range 250 Mbps to 6 Gbps)
or
Automatically mode (Redriver to retimer cross over at 1.0 Gbps)

Input signals: 640 x 480 60 p, 720 x 480 60 p (HDCP OFF)
- It does not occur with HDCP ON.
- It does not occur even at 1024 x 768 60 p. (There is a threshold in VGA ~ XGA band)

A question
Why does it occur with low resolution Retimer mode?
Please tell me the cause and measures.

In 2017 input the VGA signal with TMDS 171. When used in Retimer mode,
Noise occurred on the screen. At this time, the register of the charge pump was not ON.

Does it occur with the same contents on SN65DP159?
Regarding the image of noise, I will send it if you can tell me the destination.

Thank you.

  • 0
    TI__Guru 60870 points
    Hi Ishii-san,

    Yes, the same issue seen with the retimer at low resolutions would occur with the DP159. The same workaround of adjusting the charge pump would apply to this device as well.

    Regards,
    JMMN
  • 0 in reply to JMMN
    Genius 3945 points
    Hello.

    JMMN-san.

    Thank you for answering

    Even with SN 65 DP 159, the same phenomenon as TMDS 171 may occur.
    It is okay.

    TMDS 171 received advice to make the following settings.

    Write 0x01 to register 0xFF. To select Page 1

    Write 0x23 to register 0x00. To set A_LOCK_OVR (fixes a potential issue with retimer mode at very low resolutions)

    Write 0x7F to register 0x02. Increase the charge pump current

    Write 0x01 to register 0x01. Enable the charge pump 　

    Write 0x03 to register 0xA4. Set register overrides

    Write 0x00 to register 0xFF. To select Page 0

    SN665DP159 can not find similar items in the register map.
    How can I set it?

    Thank you.
  • 0 in reply to Masazumi Ishii
    TI__Guru 60870 points
    Page 1 registers are not documented in the TMDS171 datasheet or the DP159 datasheet, but the same register accesses used for the TMDS171 issue will apply to the DP159.

    Regards,
    JMMN
  • 0 in reply to JMMN
    Genius 3945 points

    Hello.   

    JMMN-san

    thank you for your answer.

    We carried out the same method as TMDS171.
    However, it was not improved

    We improved as a result of the following settings.

    <Changes>

    Changing Rx side Retimer mode on board

    DEV_FUC_MODE: 0x11 → 0x01 (Default setting)

    (Retimer (full range) → Automatic redriver to retimer crossover at 1.0 Gbps)

    * Tx side Retimer of board is set to Automatic redriver to retimer mode (no change)

    * Input signal 640 x 480 60 p, 720 x 480 60 p (HDCP ON / OFF) confirmed

    I have a question.

    Q1
    In the above, cross over point mode is changed with 1 Gbps as the boundary.

    How does this specifically detect the signal?

    Q2

    For signals below 1.0 Gbps, reception will be in Redriver mode
    In this case, do you have any problems or concerns?

    Thank you.

  • 0 in reply to Masazumi Ishii
    TI__Guru 60870 points
    A1. The device determines redriver / retimer crossover based on the received clock speed.

    A2. For very low resolution, we see none of the issues in redriver mode that were reported in retimer mode. Also, redriver mode has lower power consumption.

    Regards,
    JMMN