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STM32F401RE: Where does CK_INT (Internal Clock) come from?

henk van winkoop

Hi,

Using the STM32F401RE uC I wonder where the clock signal CK_INT is originating from as is shown in a Timer1 figure. I searched al the reference manual but did not find it. As my SysClk is 30MHz, checked with the MCO2 output by oscilloscoop and all AHB and APB prescalers are set to zero, Timer1 is clocked with 15MHz as I can check by toggling a GPIO on the update interrupt (TIM1_UP_TIM10_IRQHandler) with reload value of 10.000. It should be 30MHz. Do I mis some divider?

Thanks

Henk

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  • 0 in reply to Clive Unspecified

    Hi,

    thanks for your comment.

    I measured the time between 2 toggles being 666ns so the Timer1 input klok would be 666us divided by preload value 10.000 making it 66,6ns or 15MHz.
    I found the origin of the problem. The Timer1 prescaler was set to 1 by accident. I always make this mistake. Setting the prescaler value to 1 makes it divide by 2. (the prescaler value is NOT the divider value...) After setting it to 0 the toggle time is now 333us which confirms that SysClk indeed is 30MHz.

    Thanks anyway!

    (love timers if they do understand me...)

Reply
  • 0 in reply to Clive Unspecified

    Hi,

    thanks for your comment.

    I measured the time between 2 toggles being 666ns so the Timer1 input klok would be 666us divided by preload value 10.000 making it 66,6ns or 15MHz.
    I found the origin of the problem. The Timer1 prescaler was set to 1 by accident. I always make this mistake. Setting the prescaler value to 1 makes it divide by 2. (the prescaler value is NOT the divider value...) After setting it to 0 the toggle time is now 333us which confirms that SysClk indeed is 30MHz.

    Thanks anyway!

    (love timers if they do understand me...)

Children
  • 0 in reply to henk van winkoop

    The Prescaler and Period values are both end values for counters, and act as dividers

    ie

    Prescaler = P - 1; // Always 16-bit integer
    Period = Q - 1; // 16 or 32-bit depending on counter

    UpdateFreq = INT_CLK / (P * Q)

    I don't expect the processor to interrupt at MHz rates

    The timer channels can be set in toggle mode, this doesn't require interrupts.