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Original question:

LMK61E2: Calculating the Divider values

LMK61E2: Use of DEV_CTL register

John Miles
Prodigy 90 points
Part Number: LMK61E2
Other Parts Discussed in Thread: LMK61E07

I've been able to shut down the LMK61E2 PLL by setting the PLL_PDN bit in DEV_CTL (R10), but haven't been able to (reliably) restore operation without a power cycle.  Is there any particular trick to that? 

I've tried resetting SWR2PLL without any luck.  The documentation AUTOSTRT bit (which remains set) suggests that "a device reset can be triggered by ... writing to the RESETN_SW bit," but there seems to be no mention of RESETN_SW elsewhere in the data sheet:

Adding to the confusion, your LMK61E2 Oscillator Programming Tool doesn't appear to access the R10 register at all.

Is there better documentation for this somewhere?  I've noticed that the LMK61E07 data sheet is somewhat more up-to-date than the one for the LMK61E2, but it still doesn't offer any clues about resetting after setting the PLL_PDN bit.

  • 0
    TI__Genius 9920 points

    Your figures didn't show. Can you update them again?

    I sent a notice to our US team. They will reply you later.

  • 0 in reply to Shawn Han
    Prodigy 90 points

    Hi, Shawn -- The images were just copies of the table from section 8.7.1.7 of the data sheet, showing the PLL_PDN bit in R10, and a screencap of the raw register page in your programming tool that shows R10 missing altogether.  If they don't show up this time, just refer to those sources directly.

  • 0 in reply to John Miles
    TI__Genius 16845 points
    Hi John,

    Why do you want to disable the PLL using the DEV_CTL register? If you simply want to enable the output, LMK61E2 has an output enable pin that is intended for disabling the output.

    These fields were hidden in the GUI because they aren't ever really needed in the application. I personally haven't looked into this issue before, but i can recommend some things to try. Based on the datasheet R10 description, one thing to check is that you have not overwritten the autostart bit ( R10.7 = 1 ) .

    Kind regards,
    Lane
  • 0 in reply to Lane Boyd
    Prodigy 90 points

    I didn't bother connecting the OE pin to anything because the data sheet said there was a register bit that did the same thing. :)  And yes, autostart is set to 1, as noted previously.

    The ability to disable the PLL isn't especially critical in this case, it just makes it more convenient to drive this particular board from an external signal generator.  I can accomplish the same thing just by unsoldering a ferrite bead, but it would have been handy to be able to do that under software control. 

    Speaking more generally, of course, life is easier for everyone concerned when the various bits do what the data sheet says they do.  This could still be a case of user error, of course, but it's suspicious that R10 isn't supported by the software, while its description in the data sheet refers to other registers that aren't documented at all.