# Stm32 timer calculator

• STM32 Timer Interrupt HAL Example – Timer Mode LAB
• STM32 timer and interrupts configuration with STM32CubeMx utility.
• ADC conversion Time/Frequency Calculation in STM32
• STM32 Timers
• STM32 Basic Timer in Interrupt & PWM mode
• TIM3 ARR Gives Regular Interrupts on the STM32F4
• ## STM32 Timer Interrupt HAL Example – Timer Mode LAB

Thus, this method of finding the timer clock should work regardless of how I have the clocks configured. What will change are the considerations below about he range of values that are reasonable to expect from the timer.

This is a 16 bit counter that simply counts up to the value in the PSC register and wraps around. The overflow from that is what drives the actual counter, CNT.

A value of zero in PSC effectively passes the input clock straight to the counter. It is safe to change the prescaler at any time since writes are buffered and the new value will be written at the next overflow. The prescaler then can divide the input clock by any value from 1 to Suppose the input clock frequency to the prescaler is 72MHz.

It would be possible to get the counter input frequency down to as little as Hz. Exact divisions, of course will be subject to integer rounding and a lot of specific frequencies may not be possible without some juggling of oscillator values.

Thus, to get a division by 10, the PSC register must get the value 9; to get a division by , the PSC register gets the value Optionally, an event can be triggered that fires off an interrupt.

The longest interval comes when ARR is loaded with the value With a 72MHz input clock, that amounts to once every 59 seconds or so. Irritatingly, it is just short of once every minute.

Clearly, there are several pairs of PSC and ARR values for any given final frequency and so more than one way to get the exact frequency desired.

That is an event every 25us. Perhaps I want to update a Direct Digital Synthesiser or sample some sensors. Or something. It often makes sense to factor the final frequency into a pair of numbers. One value will go in the prescaler and on in the reload register. In this case the numbers are pretty easy.

I can divide the 72MHz clock by 72 to give me 1MHz into the counter — an interval of 1us — and then set the ARR to generate an event after 25 counts. I could, for instance have left the prescaler at 1 and set the ARR to generate the event after counts. The result would be the same but it is no longer easy to think in terms of intervals as multiples of 1us. Now if the requirement changed to one event every 30us, the first set of values makes this much more simple. How do decide the register values Frequency domain If the problem statement is given in terms of an event frequency it might be better to stay in that domain unless the frequency is some nice simple value like the 40kHz above.

Otherwise, calculate the total division factor needed to get the final frequency from the timer input clock and then decide how or whether to factor is out into multiple values. If the divisor is in the range 1 to , you can set the prescaler to 1 and just put the divisor into the ARR. Otherwise look for easy factors. Of course, you could write a function to calculate appropriate values for you. This is an exercise left to the reader. Again, if I have a requirement for an event every 20us, it would be easiest to think in terms of arranging for a 1MHz click into the counter and then to set the ARR for the number of 1us counts I need.

Given an event interval of 3.

## STM32 timer and interrupts configuration with STM32CubeMx utility.

The table below summarizes some common features of STM32 timers. From all of these info we can draw the versatility of STM32 timers although they are not very easy to deal with in the beginning.

This is why unlike my previous tutorials on other STM32 peripherals, we will study the timers concurrently with their applications and coding. Timer Registers Before we start coding, I must point out that perhaps the most complex sets of registers in a STM32 micro belong to timer-counter modules. Another important thing to note on these registers is the fact that though all registers in an ARM micro are bit wide, for timer modules and most hardware peripherals most of the bits are reserved.

This makes handling them easy. MikroC libraries also take care some of such. Just for reference check out the register map of any timer module. I have shown one below. Design Considerations A few things should be remembered before coding and designing hardware. Individual counters, DMA and interrupts are enabled after setting up everything else. Right after power on reset every bit of internal registers of a STM32 micro are in their default reset values.

For timer registers the default is all zeroes, meaning everything disabled. Usually this is the case for most internal hardware peripherals. However if you need to change stuffs on the fly, you better reset all settings just to avoid running down to the jaws of a software bug or unprecedented results.

If accuracy is not very important, timers can be used for general time-keeping purposes. No doubt timers are accurate than wasteful delay functions but they are not good as dedicated RTCs.

AFIO block should be enabled even if remapping is not used. When using input capture mode, be sure of the maximum input voltage level of an incoming waveform. I will however strongly suggest not to cross the VDD limit, typically 3.

Simply do not exceed the specified GPIO electrical specs. This is very important. Be aware of clock system prescalers, multipliers and clock sources. Remember APB2 bus peripherals can run at maximum system clock speed while APB1 bus peripherals are limited to half of that speed. Since internal clock speed of each timer is dependent on its APB bus speed, it is a must know to which APB bus a given timer belongs.

I have shown an example below. I chose this micro as it has all types of timer I discussed, eight timers — two advance timers, two basic timers and four GP timers. The board on which it is embedded is also neatly designed with proper readable labels — simply a nice STM32 development board. Time Base Generation This is most basic use of a timer. For this purpose we can use any timer but I recommend using either GP timers or basic timer if any.

There is no specific reason for this recommendation. It is just my way of using STM32 timers — use things that have been designed for their purposes. For making time base generators we need to follow a few steps and the overall thing is very easy. We will use interrupt-based method. First we need to determine which timer we will be using and what should be the frequency of the timer interrupt.

Repetition counters are available only in advanced timers only. We can use the following formula for determining interrupt rate: RCR will be zero unless used or available and so generally the formula will be: TIMx clock is dependent on APB bus clock.

Finally we will be enabling timer interrupts and the counter module itself. Sometime along its path in the world of embedded systems, MikroElektronika MikroE , a well-reputed microcontroller-based hardware and software solution provider, developed a free tool called Timer Calculator. This tool made life easy. We can use it to generate codes necessary for timer interrupts. If we have fairly some sound idea of how things are working inside a STM32, we can avoid all the time-consuming, tiring silly calculations and use it to complete your job easily.

We just need to select the STM32 family, MCU clock and desired interrupt rate either in terms of time or in terms of frequency.

There are also some preset code examples than can also be used to get a head start. Timer Calculator can be downloaded from here:.

## ADC conversion Time/Frequency Calculation in STM32

The longest interval comes when ARR is loaded with the value With a 72MHz input clock, that amounts to once every 59 seconds or so. Irritatingly, it is just short of once every minute. Clearly, there are several pairs of PSC and ARR values for any given final frequency and so more than one way to get the exact frequency desired. That is an event every 25us. Perhaps I want to update a Direct Digital Synthesiser or sample some sensors.

Or something. It often makes sense to factor the final frequency into a pair of numbers. One value will go in the prescaler and on in the reload register. In this case the numbers are pretty easy.

I can divide the 72MHz clock by 72 to give me 1MHz into the counter — an interval of 1us — and then set the ARR to generate an event after 25 counts. Design Considerations A few things should be remembered before coding and designing hardware. Individual counters, DMA and interrupts are enabled after setting up everything else. Right after power on reset every bit of internal registers of a STM32 micro are in their default reset values.

For timer registers the default is all zeroes, meaning everything disabled. Usually this is the case for most internal hardware peripherals. However if you need to change stuffs on the fly, you better reset all settings just to avoid running down to the jaws of a software bug or unprecedented results.

If accuracy is not very important, timers can be used for general time-keeping purposes. No doubt timers are accurate than wasteful delay functions but they are not good as dedicated RTCs.

AFIO block should be enabled even if remapping is not used.

### STM32 Timers

When using input capture mode, be sure of the maximum input voltage level of an incoming waveform. I will however strongly suggest not to cross the VDD limit, typically 3. Simply do not exceed the specified GPIO electrical specs. This is very important. Be aware of clock system prescalers, multipliers and clock sources. Remember APB2 bus peripherals can run at maximum system clock speed while APB1 bus peripherals are limited to half of that speed. Stm32f pwm formula for Prescaller value Replacing the Counter Frequency with its formula in the Timer Prescaller Value equations yields the equation given on the left side.

Now its easy to determine the prescaller value.

## STM32 Basic Timer in Interrupt & PWM mode

Note: Pwm Resolution and Timer Prescaller are bit registers their value must not exceed Now looking at the final formula we need two things in it. Stmcube-Mx code initializing steps an generating keil MDK-ARM code I assume that you people are familiar with stmcube mx project creating process and know about the necessary steps.

We can use all four timers for generating pwm pulse width modulation signal. Each timer has fixed pins on which the pwm signal can be output called channels. Timer 1 and 2 are multiplexed with other peripherals to use their pwm function we have to make sure that the timer is not colliding with any other peripheral function. Timer 3 and 4 are stand alone and they do not collide with any other peripheral function.

### TIM3 ARR Gives Regular Interrupts on the STM32F4

So its good to use them. I am using Internal clock source so check this check box in the timer settings. I am using timer 4, channel 1 for pwm output so i selected channel 1.

### thoughts on “Stm32 timer calculator”

• 07.08.2021 at 12:06