Could anyone help me calculate TIM frequency?

[Jvan .10]

Hello everyone,

I'm using TIM3 on my Nucleo H745. If it's correct this TIM gets fed from the CPU clock, so it runs at 480MHz. That's what I thought at least.

Using these settings;

htim3.Init.Prescaler = 48000;

htim3.Init.Period = 10000;

To my calculations this should be equal to 1 second.

480.000.000 / 48.000 = 10.000 Hz

When setting the period to 10000, this means it should overflow every second, right?

Not in my case. When hooking up 2 LEDs and setting their intervals to 20000 and 40000 you would expect LED1 to blink 2x in the time LED2 blinks 1x.

They blink at almost the same rate, LED2 is just a little bit slower, which means my calculations are wrong.

Can anyone spot the mistake?

Thanks!

[KnarfB]

> When hooking up 2 LEDs and setting their intervals to 20000 and 40000

Can you explain what you exactly did? If you set timer period to 10000 it will count in interval 0-9999. Where did you set 20000, 40000?

[Tesla DeLorean · Accepted solution]

Values need to be N-1 form, ie 48000-1 and 10000-1 to divide by 480,000,000

[Jvan .10]

Thank you both, together you fixed my issue. I was wrong in my calculations from MHz to Hz