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DS250DF410: Reg 0x64 setting

Part Number: DS250DF410
Other Parts Discussed in Thread: DS125DF410


I would like to ask you a question about the value of "Reg 0x64" from my customer as below.

1) Setting value

Let me comfirm that we can set the "lock range" of the signal by this register, correct? 

As the default value of the register is 1000ppm (0xFF), is it possible to change/set the value 100ppm?

2) Setting procedure

If we can change the value, will you please tell me the register setting procedure?

Thank you for your support.

Best Regards,


    • For 1, you are correct
    • For 2, See excerpt below taken from retimer datasheet,

    The value of the PPM count for either group is computed the same way from the expected data rate in unit of Gbps, RGbps. The PPM count value, denoted NPPM, is computed by NPPM = RGbps × 1280.

    Register 0x64 should be set to a value of 0xff. This is the PPM count tolerance. The resulting tolerance in parts per million is given by TolPPM = (1 × 10-6 × NTOL) / NPPM. In this equation, NTOL is the 4-bit tolerance value loaded into the upper or lower four bits of register 0x64. 

    These tolerance values can be reduced if it is known that the frequency accuracy of the system and of the 25 MHz reference clock are very good. For most applications, however, a value of 0xff in register 0x64 will give robust performance.


    Rodrigo Natal

  • Hi Natal-san,

    Thank you for your reply.

    Sorry, about my question 2, though I checked the datasheet, I could not find the contents you listed...

    Will you tell me the page number of the datasheet (DS250DF41)?

    Thank you and Best Regards,


  • My apologies, I should have clarified. I actually took that excerpt from the DS125Df410 datasheet, which has a bit more detailed description on the retimer PPM check function. See page 15 on datasheet per link below.


    Rodrigo Natal