How to sync clocks? - STM32F429

jobrace123 · ‎2014-07-15

Posted on July 15, 2014 at 14:51

Hi

I am using STM32F429 with IAR work environment and i am trying to sync two clocks

first clock: MCO2 is configured to output 29.5MHZ by using PLLI2SCLK

second clock: LCD-TFT configured to output 14.75MHZ (half of MCO2)

watching the two clocks over an oscilloscope i can see that every time i reset the STM32F429 the two clock phase difference is changed so only once in a while i am getting the phase difference i actually need. How can i control it?

Thanks and Best Regards,

Job

Tesla DeLorean · ‎2014-07-15

Posted on July 15, 2014 at 15:32

What is the observed phase difference? 180 degrees, please diagram.

You don't have any control of the circuit elements withing the PLL, or dividers. If you want signals with specific phase placement consider using TIM peripherals.

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jobrace123 · ‎2014-07-15

Posted on July 16, 2014 at 07:08

Not the answer i was hoping for but thanks

The phase difference seems quite random

I can't use TIM. The Reason is: trying to output CVBS using an analog device chip (ADV7393) which accepts RGB digital data from the STM32F429 LTDC. it seems to work only that the ADV7393 updates its pixel data at half the rate of the LTDC clock so i am getting half the resolution.

I managed to output twice the required clock rate from MCO2 but as i mentioned it is not synced so only after several resets i am getting a perfect CVBS picture