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8 years, 5 months ago.
Why does this nucleo board lack a crystal oscillator and some other flavors have it?
Is it because there's some high quality oscillator somewhere else?
Will I be okay using a timer? How about a serial port?
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1 Answer
8 years, 5 months ago.
Hello,
The STM32 members differs from each other and it make sense that the clock strategy changes between an ultra low power device and a mainstream or high performance device.
This is even more important for low pin count devices where a choice has to be made about the pin-out configuration that would satisfy most users.
All NUCLEO have a high frequency crystal (X2) connected to the ST-Link device (on the bottom side for NUCLEO32), Its frequency is then provided to the main MCU using the MCO feature. This should answer you concern regarding the timer/serial port frequency accuracy as the main frequency actually comes from an 8MHz crystal.
The crystal you are talking about, X1, is the low frequency crystal 32.768KHz. It's primary use is for low power mode, RTC and LCD. As this crystal use the same GPIO pins as D7 and D8, it makes mode sense to implement it on low power devices only while keeping D7 and D8 free on mainstream devices like the STM32F303. The low power features can be used based on the internal, less precise low speed oscillator. Of course, if this does not fit your needs, you can always modify the solder bridges and add your own crystal to the board.
You can get more details about the implementation and schematic in the NUCLEO32 user's manual. This document also provides explanations about the solder bridges and hardware options.