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10 years ago.
Max frequency and external crystal
Hello,
i recently bought this board and encountered some issues.
1. Everywhere it says, that the frequency is only up to 100 MHz, but my board runs with a sysclk of 168 MHz. Why?
2. I soldered a 8 MHz ext. crystal on the board since the manual says so. But the 'standard' crystal according to the source files of ST would be 25 MHz. Is there any need to upgrade to a 25 MHz crystal or will the 8 MHz crystal do its job just as fine? (The board runs fine by now after changing the HSE value to 8 MHz, i just want to know if there would be any real benefits from using a 25 MHz crystal)
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1 Answer
10 years ago.
Are you sure the SystemCoreClock is running at 168MHz. The F411 can be overclocked like most CPUs but at some point it will become unreliable and random crashes or bugs will happen. The clock could be too high when you mess with the PLL settings or when the settings are for another xtal than what has been mounted. I think the first batch of nucleo boards only used the HSI internal clock (also about 8MHz), later boards had the 8MHz clock from the STlink programmmer routed to the target F4. First generation mbed libs for the nucleo all used the HSI clock and ran at slow clockrates. I think I have seen wrong default clock defines of 25MHz in some of those old libs. Later versions of the lib were fixed to run the target at rated speeds on both HSI and HSE. Make sure your mbed (source code) is up to date. The F4 can run on a 25MHz xtal, but then you should modify the code accordingly otherwise the PLL calculations will be wrong since the lib assumes 8 MHz.