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x1, x2 multiplier before TIM2 to TIM7?

picguy
Associate II
Posted on July 31, 2008 at 03:20

x1, x2 multiplier before TIM2 to TIM7?

3 REPLIES 3
picguy
Associate II
Posted on May 17, 2011 at 12:40

Looking at the STM32 Clock Tree I have SYSCLK=72 MHz. The APB1 Prescaler is set to /2 sending a 36 MHz PCLK1 to APB1 peripherals.

That same 36 MHz clocks TIM2 to TIM7.

That’s what I thought until TIM3 setup to make a 1 KHz interrupt actually made a 2 KHz interrupt. Then I saw something - - there is a x1, x2 multiplier between my 36 MHz APB1 clock and the timers.

What register does one set to specify x1 or x2? There is an equivalent x1, x2 multiplier before timer 1 and timer 8. I suspect the docs for both controls are tucked away where I can’t find them. I have looked. Silicon Valley ST support sent my request for documentation “back through Technical support� whatever that means.

Does someone here know where thicontrol is?

asterix
Associate II
Posted on May 17, 2011 at 12:40

Hi Picguy,

See attached Figure from datasheet. This is fixed by hardware internally

if the APP prescaler is <> 1 then the Timer clock is multiplied by x2.

I believe that no control is provided to software.

Regards, Magigimix.

picguy
Associate II
Posted on May 17, 2011 at 12:40

Thanks, I had an old clock tree diagram.