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8 years, 7 months ago.
Use of external crystal X3 for NUCLEO-F411RE
If I want to solder an external crystal on the X3 slot and use it as the source for clock,
1. Should I use a 8MHz crystall?
2. What code should I write to select this external crystal instead of using the internal oscillator?
3. What will the final frequency be? 96MHz?
4. How to change the speed for the microcontroller? i.e., if there is a function in mbed that I can use to get any possible speed I want, 48MHz, 16MHz, 8MHz, etc?
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1 Answer
8 years, 7 months ago.
Not sure with the F411 but the F401 that shares pretty much the same set up code does auto detect the 8 MHz external crystal if fitted (along with the loading capacitors). I believe the core frequency is 96MHz in this case.
Also applies to the 32KHz RTC crystal if you want to fit that too (optional).
Below may also apply to the F411:
The F401 has a long delay (5 seconds) to come out of reset and start the user program, may be an error in the set up as this can be set back to 500mS and does work for me.
It is possible to change the system clocks to different speeds. I can't see why you want to do this, however if you are trying to reduce power, currently the STM platforms on Mbed do not support low power operation to any usable degree (sleep, deepsleep). For low power operation on Mbed the Freescale KL, K20, K22F and SiLabs EFM series are far more suited. Others also but I have not tried them.