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SKada.1
SKada.1
Associate
July 26, 2021
Question

Is it recommendation to used internal RCC clock instead of external crystal.

For peripherals like SPI as HCI, I2S which clock should use RCC or external crystal?

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2 replies

TDK
TDK
July 26, 2021

HSE (high speed external crystal) will be more accurate than HSI (high speed internal oscillator), but for SPI and I2C, the extra accuracy will not matter. Not sure what HCI is.

For UART, the extra accuracy can help, but this depends on your particular clock settings. HSI is very often sufficient.

For USB, HSE is often required to meet USB timing requirements, although some chips get away with the HSI by using a clock recovery system based on packets sent by the host.

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Tesla DeLorean
Tesla DeLorean
Guru
July 26, 2021

 Host Controller Interface (HCI), frequently in a Bluetooth context.

The internal clocks usually lack any accuracy in the static modes, and also across temperature and voltage.

Things with critical requirements, like Ethernet, CAN, USB, Radio, etc the use of crystal or TCXO clocks is preferable for reliable operation and interaction with other equipment.

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