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TM4C1294NCPDT: QSSI timing in slave mode

UNA
Mastermind 7980 points
Part Number: TM4C1294NCPDT

Hi,

I have a question about timing in QSSI slave mode.
The data sheet specifies that the minimum timing of S11(TXDSOH) is 37.4ns, however it seems that S11 is output in about 22 to 33 ns in actual measurement.
TM4C1294 is used in Freescale SPI Frame Format with SPO=0 and SPH=0 at slave mode.

The measured waveform is attached below.

- TSYSCLK = 120Mhz
- SSI2Clk(4 pin): Blue
- SSI2TX(2 pin) : Green
- The SPI transfer rate is 6Mbps, and the slave outputs 0x55.

The figure below expands the third falling clock edge.

The figure below expands the fourth falling clock edge.

Although the measurement results are less than the data sheet specifications, are the data sheet specifications correct?

Best Regards,
H.U

  • 0
    TI__Guru 72500 points
    Interesting. It looks like the 37.4nS should have been the maximum delay (at 120MHz). The minimum looks like 2.5 cycles. I will need to look into this. Since most SPI implementations don't require a hold time on the changing edge, is this timing critical in your design?
  • 0 in reply to Bob Crosby
    Mastermind 7980 points

    Hi Bob,

    Thank you for your reply.

    In our final product, TM4C1294 QSSI signals are connected to external devices by connector and cable.
    The external device (SPI master) needs to know the SPI specs of our product. Therefore, I can not sell our products unless SPI slave timing is described in our specification.
    So, this issue is critical for our design. I need your help.

    Best Regards, 
    H.U

  • 0 in reply to UNA
    TI__Guru 72500 points
    Redoing the characterization and updating documentation is a lengthy process. What is the minimum documentation you need from TI? Will an e-mail from TI with the proposed corrected timings be sufficient?
  • 0 in reply to Bob Crosby
    Mastermind 7980 points
    Hi Bob,

    I understand that it takes time to revise documents.
    If TI can commit to revising the data sheet in the future, email is sufficient at this time.
    It would be even better if there is a simple letter that can prove the modification of the QSSI timing characteristics. For example, It may be like an excerpt of the data sheet.

    Best Regards,
    H.U
  • 0 in reply to Bob Crosby
    Mastermind 7980 points

    Hi Bob,

    I’m waiting for your reply.
    I want to clarify ASAP which of my measurement results and the QSSI timing characteristics described in the data sheet are correct. And I want to know the correct value of S11(TXDSOH).

    Best Regards,
    H.U

  • 0 in reply to UNA
    TI__Guru 72500 points

    Sorry for the delay. We think the timing in the datasheet is not correct and what is listed as a minimum time is indeed a maximum time. Still working on the minimum time. It looks to be about 16.5nS (at 120Mhz). What we plan to do is add this to the next publication of the errata document SPMZ850. I don't know when the next release of that document will be, but I can create a draft version with the added advisory once we nail down the true minimum time.

  • 0 in reply to Bob Crosby
    Mastermind 7980 points

    Hi Bob,

    Thank you for your dedicated support.
    I am looking forward to receiving the draft version.

    Best Regards,
    H.U

  • 0 in reply to UNA
    Mastermind 7980 points

    Hi Bob,

    Sorry for the rush.
    Could you provide the draft version by June 11th?  Because our mass production schedule is approaching.

    Best Regards,
    H.U

  • 0 in reply to UNA
    TI__Guru 72500 points

    I am sorry but I have run into some logistics issues and was not able to create a draft for you by the 11th. I hope to resolve these issues and create the draft by the end of the day June 14th.

  • 0 in reply to Bob Crosby
    TI__Guru 72500 points

    Last week I sent you a friend request so that I could e-mail a draft of the updated errata document. I am awaiting your response.

  • 0 in reply to Bob Crosby
    Mastermind 7980 points

    Hi Bob,

    I accept your friend request and sent you a private message, could you receive it?

    Best Regards,
    H.U

  • 0 in reply to Bob Crosby
    Mastermind 7980 points

    Hi Bob,

    Thank you for your response.
    I got a draft  of the errata document.

    Best Regards,
    H.U