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DS90UB948-Q1: Distinguishing between BIST and MAP in the DS90UB948.

?? ??
Prodigy 150 points
Part Number: DS90UB948-Q1


Tool/software:

Hello,

The DS90UB948 has two functions: MAP and BIST. Please explain how to distinguish between these two functions.

1. Is my understanding below correct?
- MAP: Extracts the range in which communication can be conducted normally, with EQ and SP each ranging from minimum to maximum.
- BIST: Performs a BER test at an arbitrary EQ value and outputs the number of errors.

2. Does MAP perform BIST for each EQ and SP?

3. If 1 and 2 are correct, is it sufficient to evaluate only AEQ in practice? Is the only time to use BIST when investigating the actual error rate at the EQ value set by AEQ?

  • 0
    TI__Mastermind 35415 points

    Hello,

    ?? ?? said:
    1. Is my understanding below correct?
    - MAP: Extracts the range in which communication can be conducted normally, with EQ and SP each ranging from minimum to maximum.
    - BIST: Performs a BER test at an arbitrary EQ value and outputs the number of errors.

    MAP sweeps over the EQ and Strobe (SP) range (the range of values can be changed by the user) to determine whether LOCK is stable or not at these values. If LOCK is not stable, then stable communication cannot be certain. LOCK is lost if the CLOCK0, CLOCK1, or DCA bit is incorrect in the incoming FPD-Link frame.

    MAP App Note: Link

    BIST performs a BER test at the EQ value chosen by the AEQ. The AEQ will choose an EQ value that has a stable LOCK. Keep in mind that after BIST is disabled a reset of the AEQ is needed as noted in the datasheet.

    ?? ?? said:
    2. Does MAP perform BIST for each EQ and SP?

    No. MAP is only monitoring LOCK status. BIST is not done during MAP

    ?? ?? said:
    Is the only time to use BIST when investigating the actual error rate at the EQ value set by AEQ?

    BIST is used to determine BER after MAP has been used to determine if the link has enough margin. 

    Best,

    Jack

  • 0 in reply to Jack Scherlag
    Prodigy 150 points

    Hello,

    Thank you for your response.
    I understood as follows:

    • MAP: Determines the points where LOCK is stable within the range swept by EQ and SP.
    • BIST: Performs a BER test at the EQ value selected by AEQ.

    I have two additional questions:

    1. Is my understanding correct as follows?
      Since BIST is a function used during the design stage, the product does not need to perform BIST on its own after mass production and will operate at the EQ value set by AEQ.

    2. Should BIST be conducted at multiple EQ values in preparation for changes in EQ values due to factors such as temperature and vibration (AEQ)?

    Best,

  • 0 in reply to ?? ??
    TI__Mastermind 35415 points

    Hello,

    ?? ?? said:
    Since BIST is a function used during the design stage, the product does not need to perform BIST on its own after mass production and will operate at the EQ value set by AEQ.

    The user can perform BIST during the design stage, prototype stage, or assembly stage. There is ultimately no "need" to perform BIST as long as the design conforms to the channel specifications. BIST is a tool the user can utilize to confirm that the desired BER can be met.

    ?? ?? said:
    Should BIST be conducted at multiple EQ values in preparation for changes in EQ values due to factors such as temperature and vibration (AEQ)?

    Because the AEQ will search for the EQ setting without errors, it would be best to use either longer cables or aged cables to simulate an aged cable and cable harness.

    Best,

    Jack

  • 0 in reply to Jack Scherlag
    Prodigy 150 points

    Hello,

    Thank you for your response.
    I understood the content, but I couldn't grasp the difference between LOCK by MAP and BER by BIST.

    Is my understanding correct as follows?

    • MAP: Communication is repeated for the specified dwell time, and LOCK is lost if the CLOCK0, CLOCK1, or DCA bits are incorrect.
      If LOCK is maintained at over 90% (?), it is indicated as green = OK.
    • BIST: A predetermined communication is repeated to calculate the error rate based on the number of errors that occurred.

    For example, if MAP is executed with PCLK 58.7 [MHz], Forward channel rate 2054.5 [Mbps], and dwell time 5000 [ms], the data count is 10^-11. However, since only CLOCK0, CLOCK1, and DCA are being checked, it does not mean that the BER is 10^-11.

    Best,

  • +1 in reply to ?? ??
    TI__Mastermind 35415 points

    Hello,

    ?? ?? said:
    MAP: Communication is repeated for the specified dwell time, and LOCK is lost if the CLOCK0, CLOCK1, or DCA bits are incorrect.
    If LOCK is maintained at over 90% (?), it is indicated as green = OK.

    LOCK has to be constantly maintained over the dwell time for the EQ/SP combination to be OK (green). If there is any loss of lock, then the EQ/SP combination is not considered passing.

    ?? ?? said:
    • BIST: A predetermined communication is repeated to calculate the error rate based on the number of errors that occurred.

    For example, if MAP is executed with PCLK 58.7 [MHz], Forward channel rate 2054.5 [Mbps], and dwell time 5000 [ms], the data count is 10^-11. However, since only CLOCK0, CLOCK1, and DCA are being checked, it does not mean that the BER is 10^-11.

    You are correct on the BIST definition and the limitation of MAP. MAP cannot be used to determine BER since the video data is not checked for correctness.

    Best,

    Jack

  • 0 in reply to Jack Scherlag
    Prodigy 150 points

    Hello,


    I have a good understanding of the differences between MAP's LOCK and BIST's BER.

    In the design evaluation, we first execute MAP to confirm that LOCK is stable (which ensures stable communication), and then we conduct BIST with the EQ value determined by AEQ to check the error rate.

    Thank you for the prompt and detailed response.

    Best,