AnsweredAssumed Answered

PLL using external crystal oscillator

Question asked by Chinmay Gore on Apr 13, 2017
Latest reply on May 3, 2017 by Dezheng Tang

Hi All,

I am using LPC11E68 and trying to run the PLL on external crystal oscillator of 12MHz.

It works fine when the PLL input clock source is IRC oscillator, but doesn't work when it switched to crystal oscillator.

Here in my code, I have followed the steps which I have given below:

1. Setup IRC oscilltor as input clock source to PLL. Got PLL output of 12MHz by setting the appropriate values. Selected Main clock source as PLL output.

2. Enable clock to IOCON Block.

3. Set up PIO2_0 and PIO2_1 as function 1(XTALIN and XTALOUT) and enabled Analog mode.

4. Now I set the crystal oscillator to input clock source to PLL.

   LPC_SYSCTL->SYSPLLCLKSEL  = 1;

and updated the clock source .

5. Powered down PLL power, set the msel and psel values and then powered the PLL up.

6. Waited for PLL lock

7. Set the system clock divider as 1.

8. Disabled bypass bit and selected freq range: Low. 1 - 20 MHz in SYSOSCCTRL

8. Selected Main clock source as PLL output.

 

Still it is not working on external crystal.

I would be grateful if anyone could help me in this regards.

Thank you!

- Chinmay

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