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TDES960: CX3 and SerDes I2C communication problem

kanna
Intellectual 335 points
Part Number: TDES960
Other Parts Discussed in Thread: TSER953,

Tool/software:

We are working on a USB-based system with a TI Serializer and Deserializer (SerDes) using FPD-Link. The system includes CX3 as the I2C master, communicating with an MCU over the SerDes link.

Issue Observed:

During I2C transactions, we observed bit loss and NACK issues depending on the clock speed and delay configuration. Below are the different methods we tested:

  1. I2C Clock = 400 kHz (CX3) without delay for each MCU transaction
    • Issue: Bits were missing; for example, if we sent 0x01FF, the serializer side received only 0xFF.
  2. I2C Clock = 100 kHz (CX3) without delay
    • Issue: The serializer responded with NACK.
  3. I2C Clock = 100 kHz (CX3) with 280ms delay per MCU transaction
    • Result: We received ACK, but required a significant delay for communication.
  4. I2C Clock = 100 kHz (CX3) + Fast-Plus Mode (SER/DES side, adjusted high/low time)
    • Result: Communication worked without requiring delay for MCU transactions.

Questions:

  1. What could be the root cause of the bit loss and NACK issues in our initial tests?
  2. Is our final implementation (100 kHz CX3 + Fast-Plus I2C mode on SER/DES) a correct and stable solution?

Any insights or similar experiences would be helpful. Thanks in advance!

  • 0
    TI__Guru 66810 points

    Hello, 

    Monday 2/17 is a US public holiday, support will resume on Tuesday 2/18. Thanks for your patience. 

    Regards, 

    Logan

  • 0 in reply to Logan Cummins
    TI__Genius 16230 points

    Kanna,

    We will reply in the next 24hrs.

  • 0
    TI__Mastermind 28040 points

    Hello Kanna,

    A couple questions to get a bit more information on your setup.

    1) Are you using our TDES960/TSER953 EVMs in your initial testing? Or did you already build custom PCBs with our TDES960/TSER953 devices populated?

    2) According to App Note SLVA689, you can calculate the appropriate pull-up resistor to use, based on the I2C bus capacitance and the I2C speed implemented in the system. It's possible that maybe the I2C pull-up resistor used is only suitable for Fast Mode Plus operation. If you probe the I2C lines on the SER/DES board, do you see any missing bits?

    Best,

    Justin Phan