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DS90UB927Q-Q1: About SCL frequency

user5163865
Genius 3980 points
Part Number: DS90UB927Q-Q1
Other Parts Discussed in Thread: DS90UB928Q

Tool/software:

Hi,

I have a question about the SCL frequency.

Customer's evaluation method
An I2C master is connected to the DS90UB927Q (SER), and remote I2C communication is being performed with a device connected to the DS90UB928Q (DES) via FPD-Link.

Question about the SCL frequency

1) The I2C-SCL frequency output from the DES is fixed at about 66kHz regardless of the input to the SER.

   Is this due to the settings of the registers 0x26 (SCL High Time) and 0x27 (SCL Low Time)?


2) The default values ​​of the above 0x26 and 0x27 registers are 0x83=131 and 0x84=132, respectively.

  When calculated from this, the SCL frequency is about 76kHz, but the actual measured value was 66kHz. Why is there a difference?


3) Can the SCL frequency output from the DES be set by a method other than the above?

4) For example, if the SCL input to SER is 100 kHz, won't the output also automatically become 100 kHz?


Best regards,
Hiroshi

  • +1
    TI__Guru 66810 points

    Hi Hiroshi,

    user5163865 said:

    1) The I2C-SCL frequency output from the DES is fixed at about 66kHz regardless of the input to the SER.

       Is this due to the settings of the registers 0x26 (SCL High Time) and 0x27 (SCL Low Time)?

    DES SCL output frequency (operating as a proxy master) depends on the SCL high/low time registers, it has nothing to do with the SER side I2C rate.

    user5163865 said:


    2) The default values ​​of the above 0x26 and 0x27 registers are 0x83=131 and 0x84=132, respectively.

      When calculated from this, the SCL frequency is about 76kHz, but the actual measured value was 66kHz. Why is there a difference?

    SCL/I2C rate is based on the internal always on clock within the device, which can have up to 10-20% deviation. This is why there is a delta between the 76kHz and 66kHz.

    user5163865 said:

    3) Can the SCL frequency output from the DES be set by a method other than the above?

    No, only above method.

    user5163865 said:


    4) For example, if the SCL input to SER is 100 kHz, won't the output also automatically become 100 kHz?

    DES and SER I2C bus is indpendent of one another. Technically, one side can be 400kHz while the other is 100kHz for example.

    Regards,

    Logan

  • 0 in reply to Logan Cummins
    Genius 3980 points

    Logan-san

    Thanks a lot.

    Best regards,
    Hiroshi