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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!