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LMX2615-SP: Toggle FCAL_EN bit in R0

Bill Grove
Prodigy 120 points
Part Number: LMX2615-SP

Does toggling the FCAL_EN bit require 2 writes to register R0?  If so should there be a delay between these writes and how long?  In using the TICS Pro - LMX2615 tool, toggling the FCAL_EN (to lock the VCO after changing frequency) shows 2 writes in the log display:  "Wrote Register R0 as 0x002110"  and "Wrote Register R0 as 0x002118".  Here we can see that bit D3 is toggled from '0' to '1' with the 2 writes.

I am wondering in developing software driver code is it sufficient to just write a '1' to the FCAL_EN bit upon changing frequency or should the driver perform 2 writes as described above?

thanks,

Bill

  • 0
    TI__Guru** 107680 points

    Hi Bill.

    Right, after programming it to a new frequency, simply write R0 once (with FCAL_EN=1) to initiate a VCO calibration. 

  • 0 in reply to Noel Fung
    Prodigy 120 points

    It sounds like the VCO calibration hardware within the chip is basically triggered whenever the FCAL_EN bit is set to '1'.  It must then clear itself (to '0') after some time such that the bit can be set to '1' again at some point.  I just want to make sure this is how it works.

    thanks,

    Bill

  • 0 in reply to Bill Grove
    TI__Guru** 107680 points

    Hi Bill,

    No, it is not self-clearing. The RESET bit does. 

    My suggestion is keep FCAL_EN=1 all the time, whenever you want to do a calibration, program R0 once. 

  • 0 in reply to Noel Fung
    Prodigy 120 points

    Note that we are using the partial assist mode and will be changing frequency very often. The data sheet says to program FCAL_EN (R0[3]) = 1, each time the frequency is changed.  My concern is that prior to the next time we change frequency there was no action to program the FCAL_EN bit back to '0'.  Therefore FCAL_EN always equals '1'.  The question is: Is it ok to write a '1' to FCAL_EN even though it is already equal to '1'. Is it ever necessary to set it to '0'?  Put another way, if we change frequency and FCAL_EN already equals '1', is it necessary to write a '1' to it again?

    Note that the TICS Pro - LMX2615 tool requires the toggling of the FCAL_EN bit (to lock the VCO after changing frequency) and shows 2 writes in the log display, the first write sets FCAL_EN = 0, the second write sets FCAL_EN = 1.  This is done every time the frequency is changed with this tool.

  • 0 in reply to Bill Grove
    TI__Guru** 107680 points

    Hi Bill,

    Keep FCAL_EN=1 all the time and program R0 whenever a calibration is required.

    For example, if R0 = 0x251C (FCAL_EN = 1). After changing the N-divider to a new value, program R0 (=0x251C) once to initiate calibration so that the chip can lock to the new frequency with the updated N-divider value.

  • 0 in reply to Noel Fung
    Prodigy 120 points

    Hi Noel,

    thank you, this clarifies my concern.

    Bill