HSI vs HSE for CAN

krishr · ‎2024-07-10

Hi,

On an Stm32f4 based board, we have the external crystal (8MHZ) mounted. The Firmware however uses HSI clock.

Does the HSI drift have an impact on CAN communication with another device over a long period of time(say weeks)? Is it recommended to use HSE instead?

Thank you in advance for your inputs.

SofLit · ‎2024-07-10

Hello,

We don't recommend to use any of the RC-based internal clock sources such as HSI/MSI/CSI etc for CAN communication as it can drift over time. This is mainly when Normal mode is used. These internal clock sources may impact communication performance as they could be influenced by different factors (temperature/voltage/reflow effects/ mechanical effects etc.). We recommended using HSE with an external crystal or another precise clock source (Ex: crystal oscillator) in bypass mode.

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LCE · ‎2024-07-10

I don't know how "good" the F4's HSI is, on F7 and H7 it is quite jittery, so with these I wouldn't use the HSI for anything.

But what do the HSI specs say about drift? Anything in the datasheet?

SofLit · ‎2024-07-10

Hello,

We don't recommend to use any of the RC-based internal clock sources such as HSI/MSI/CSI etc for CAN communication as it can drift over time. This is mainly when Normal mode is used. These internal clock sources may impact communication performance as they could be influenced by different factors (temperature/voltage/reflow effects/ mechanical effects etc.). We recommended using HSE with an external crystal or another precise clock source (Ex: crystal oscillator) in bypass mode.

To give better visibility on the answered topics, please click on "Accept as Solution" on the reply which solved your issue or answered your question.