# RFSoC 4x2 PLL Lock Leds don't turn on

**URL:** <https://discuss.pynq.io/t/rfsoc-4x2-pll-lock-leds-dont-turn-on/8063>\
**Category:** Support\
**Created:** [February 19, 2025, 4:14pm UTC](https://discuss.pynq.io/t/rfsoc-4x2-pll-lock-leds-dont-turn-on/8063 "2025-02-19T16:14:43Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![mtsanic](https://avatars.discourse-cdn.com/v4/letter/m/bb73d2/32.png) [@mtsanic](https://discuss.pynq.io/u/mtsanic)\
**Post date:** [February 19, 2025, 4:14pm UTC](https://discuss.pynq.io/t/rfsoc-4x2-pll-lock-leds-dont-turn-on/8063/1 "2025-02-19T16:14:43Z")

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Hi,

I am trying to change LMK and LMX clocks on the RFSoC 4x2. I used TICS PRO to get the registers.

When I check the ADC/DAC tile PLLLockStatus from the board, it shows as 2 (XRFDC\_PLL\_LOCKED in C code). The TICS PRO software also shows as PLLs are Locked. However, the LED indicators on the RFSOC 4x2, don’t turn on. I am assuming that my PLLs are locked, but I am concerned about the LED indicators.

Has one faced with this issue before?

Best

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**Author:** ![cathalmccabe](https://sea1.discourse-cdn.com/flex019/user_avatar/discuss.pynq.io/cathalmccabe/32/3348_2.png) [@cathalmccabe](https://discuss.pynq.io/u/cathalmccabe)\
**Post date:** [March 4, 2025, 10:01am UTC](https://discuss.pynq.io/t/rfsoc-4x2-pll-lock-leds-dont-turn-on/8063/2 "2025-03-04T10:01:34Z")

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From the [LMX2594RHAR datasheet](https://www.ti.com/lit/ds/symlink/lmx2594.pdf?ts=1741081743531&ref_url=https%253A%252F%252Feu.mouser.com%252F), the MUX OUT pin is configurable to show the lock, or to be used to readback info from the chip. It is possible you have changed the config for this pin which is why the LEDs may not be showing the lock.  
If you readback in SW that it is locked, I would go ahead with that.

Cathal

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**Author:** ![system](https://sea1.discourse-cdn.com/flex019/user_avatar/discuss.pynq.io/system/32/2_2.png) [@system](https://discuss.pynq.io/u/system)\
**Post date:** [April 24, 2025, 1:52pm UTC](https://discuss.pynq.io/t/rfsoc-4x2-pll-lock-leds-dont-turn-on/8063/3 "2025-04-24T13:52:35Z")

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