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LMX2571: Switching between F1 and F2

Jejomar Ildefonso
Genius 9520 points
Part Number: LMX2571

Hi Team,

Need your inputs to clarify our confusions with regards to switching between F1 and F2 of LMX2571. The second paragraph of section 8.1.2 of the datasheet implies that the switching can be made by writing on the F1F2_CTRL, and F1F2_SEL registers.

Writing "1" on F1F2_CTRL sets the control to TrCtl pin. However, what confuses us is its relation to the F1F2_SEL. Are these controls independent of one another? Are they somewhat "overriding" what is configured to the other?

For example, assuming that F1F2_CTRL = 1 at the time F1F2_SEL=1 (selecting F2 config registers), would this output the F2 parameters? If so, then toggling TrCtl pin can "override" F1F2_SEL register settings and switch the frequency to F1?

If this is the case, can the F1F2_SEL settings do the same "overriding" to the TrCtl pin?

Would really appreciate your clarifications. Thanks in advance!


Kind Regards,

Jejomar

  • 0
    TI__Guru** 109000 points

    Hi Jejomar,

    After programming R0 with F1F2_CTRL = 1 and F1F2_MODE = 1, the output frequency (F1 or F2) and active output port (Tx or Rx) will be depending on the TrCtl pin.

    Whenever F1F2_CTRL = 0, toggling TrCtl has no effect.

  • 0 in reply to Noel Fung
    TI__Genius 9520 points

    Hello Noel,

    Thank you for your help! We just have two additional questions for clarity.

    1. Does this mean the F1F2_SEL registers won't have any effect as well when F1F2_CTRL = 1? If yes, would there be something we can look at to properly identify what initial output frequency does the initial state of the TrCtl pin would correspond to?

    2. If you look at the 2nd paragraph of section 8.1.2 in the datasheet, it says: "To switch frequency using the TrCtl pin, set F1F2_CTRL to 1. F1F2_SEL selects the output frequency for the current status".

    From here our assumption is that this "current status" set by the F1F2_SEL means the initial output frequency in line with the current state of the TrCtl pin. Then toggling TrCtl pin would switch to the other frequency.

    We may be wrong on our interpretations or there might be other parts of the datasheet that may have been overlooked. But we would really appreciate your clarifications on this. Thanks!

    Kind Regards,

    Jejomar

  • 0 in reply to Jejomar Ildefonso
    TI__Guru** 109000 points

    Hi Jejomar,

    TrCtl will toggle F1F2 and TxRx port, we have to manually map the frequency register set (F1 or F2) to the status (HIGH or LOW) of the TrCtl pin. For example;

    Given F1F2_CTRL = 1, RXTX_CTRL = 1 and RXTX_POL = 0. When TrCtl pin = 0, TX port is the active output port.  Then, we set F1F2_SEL = 0 to assign TX port output frequency = F1. 

    now we set TrCtl pin = 1, the active port becomes RX and the output frequency will be switched to F2.