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LMK05318B: Register write sequence for PPM offset using absolute DCO adjust

david royle
Intellectual 585 points

Part Number: LMK05318B

Moving output frequency a few ppm using absolute DCO adjust involves writing the DCO numerator which is 5 registers long (40 bits). 

Is a specific register sequence is required to ensure a hitless switch?

  • 0
    TI__Expert 8665 points

    Hello David,

    To ensure a hitless switch, please set the below control to Hitless switching (default).

    or

    Write 0x2D to register 0xFC.

    Regards,

    Kia Rahbar

  • 0 in reply to Kia Rahbar
    Intellectual 585 points

    Please address my specific question.

  • 0 in reply to david royle
    Intellectual 585 points

    For example, if the new value takes effect after the least significant byte is written, then I would have to write the registers from most significant to least significant. Of does it just wait until all 5 have been written?

  • +1 in reply to david royle
    TI__Expert 8665 points

    Hello David,

    You must write the registers from most significant byte to least significant byte. Once the least significant byte is written the DCO write will occur. The new value only takes effect once the least significant byte is written to.

    You could skip writing to the x (1,2,3,4) number of most significant bytes if their value is not changing between writes, but if all 5 bytes have a different value in the next write, then you will have to write to all of them.

    For example if you want to write a value of 0x0C to for the DCO adjustment, then you will only need to write to the least significant byte. But if you want to write a value of 0xCCCC, then you will need to write to the two least significant bytes. Then if you want to write 0x0C you will have to assign a value of 0x00 to the second byte again and then set the least significant byte to 0x0C for the new value of 0x0C to be written to the device.

    Regards,

    Kia Rahbar