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DS90UH925Q-Q1: DS90UH925Q-Q1 720p 24-bit Color FPD-Link III Serializer with HDCP

Mennatallah Saeed
Prodigy 20 points
Part Number: DS90UH925Q-Q1

Tool/software:

Using DS90UH925Q-Q1 720p 24-bit Color FPD-Link III Serializer with HDCP, we noticed an undefined behavior when the following steps were executed: 

* Scenario #1: 

- Writing to the reset register (0x01) a value of (0x03) which sets the first 2 bits (Digital reset 0 and digital reset 1), then trying to read any other register; for example: ( Configuration [0] :0x03 with default value of 0xD2 and our we configured it with 0xD3 according to our project need), we find the value of the register is back to its default value as expected. 

* Scenario #2: 

- Writing to the reset register (0x01) a value of (0xFF) which sets all the register bits including the reserved ones, after that when we try to read any register; for example: ( Configuration [0] :0x03), we find the value of the register is 0x00 not even the default value. 

We need to understand what happens when we write 0xFF to the reset register because all other registers became unresponsive after that. 

Thank you.

  • 0
    TI__Genius 12270 points

    Hi Mennatallah,

    Mennatallah Saeed said:
    (0x01) a value of (0xFF) which sets all the register bits including the reserved ones

    It may not be recommended to set reserved registers and leave these to the default values, as this will usually produce unexpected results. The bit that you may be interested in for the reset (0x01) register is bit 7 -> Remote Auto Power Down. This details that the device will automatically power down when no bidirectional link is detected.

    It is recommended to only use the first two bits for resetting the device, unless you need this auto power down feature. It is also not recommended to change any reserved registers from the datasheet.

    Best,

    Miguel

  • 0 in reply to Miguel Bolante
    Prodigy 20 points

    Hello Miguel, 

    Thank you for the clarification! 

    Though I have a question, will you clarify further the difference between Bit 0 and Bit 1 and if we are to re-enable the serializer again shall we set both bits together or on of them shall be enough ? 

  • +1 in reply to Mennatallah Saeed
    TI__Genius 12270 points

    Hi Mennatallah,

    A Digital RESET1 (0x01[1]) will reset the entire digital block including the register configurations. For example, 0x03 changing from 0xD3 to 0xD2 upon RESET1.

    A Digital RESET0 (0x01[0]) will only reset the digital block, register assignments should remain at the configured values.

    You will not need to use both every time, only one or the other depending on the requirement. RESET1 will include register resets AND digital block reset, so no need to run a RESET0 after.

    Hope this helps! 

    Best,

    Miguel

  • 0 in reply to Miguel Bolante
    Prodigy 20 points

    Hello,

    Thank you Migual for the  clarification. now the use case is clear.

  • 0 in reply to Mennatallah Saeed
    TI__Genius 12270 points

    Hi Mennatallah,

    Happy to help! Closing out this thread now, thanks.

    - Miguel