Prescaler and timers

[eixp12]

Posted on March 30, 2012 at 10:17

How can I configure

the

Port A

prescaler

to read

every 5

seconds.

What is the

formula

that is used

?

Is there a

document that explains how

I set

the timers

?

[Tesla DeLorean]

Posted on March 30, 2012 at 14:50

I've always found reading the TECHNICAL MANUALS to be quite adequate

Where

  TIM_TimeBaseStructure.TIM_Prescaler = X - 1;

  TIM_TimeBaseStructure.TIM_Period = Y - 1;

UpdateRate = (TIMCLK / X) / Y;

For 5 Seconds, and 72 MHZ, you must factor 72000000 * 5 into two 16-bit values (ie less than 65536)

= 5 * 72000000

= 360000000

= 36000 * 10000

Prescale = 36000 - 1;

Period = 10000 - 1;

[eixp12]

Posted on March 30, 2012 at 18:05

The TIMClK is the value of the Sysclock or AHPB1 stm32f4discovery?

 Then the prescaler must always be less than 65536 right.

When we multiply 5 * 72000000 = 360000000 which means?

[Tesla DeLorean]

Posted on March 30, 2012 at 18:39

TIMCLK will depend on which TIM you use, and the clock settings on your system. I assumed 72 MHz based on how the STM32F1xx chips work.

On an STM32F4 it's presumably 168 MHz or 84 MHz. And you also have a couple of 32-bit period counters.

Assuming 5 seconds at 168 MHz, we have

= 5 * 168000000

= 42000 * 20000

I don't presume to know what settings you have, refer to the clock tree and settings.

You are trying to count the number of clock ticks over 5 seconds. Realistically you could have the interrupt at a more frequent rate, and then count off 5 seconds.

[eixp12]

Posted on March 30, 2012 at 18:55

thank you

I'll try to implement