Stm32f103 Pwm(Pulse width modulation) signal generation using internal timers, keil MDK-ARMv6 and Stmcubemx Ide

This tutorial is about generating pwm (pulse width modulation) signal with stm32f103 microcontroller using its internal hardware timers. Stm32f103 microcontroller components/peripherals initialization code is generated using stmcubemx ide and code is written and compiled in keil MDK-ARMv6 ide. A simple led is derived on a fixed pwm signal output. Led dims and blinks according to the duty cycle and frequency that a particular pwm pin is outputting. A single Pwm signal is generated/Outputted in the tutorial, but you can generate multiple pwm signals with the same method and settings.

I am going to output a 1 Hz frequency and 50% duty cycle pwm(pulse width modulation) signal using timer-4 of stm32f103 microcontroller. Timer-4 channel-1 is used to output signal. Channel-1 corresponds to PB6 pin of stm32f103 microcontroller. At PB6 an led is connected on which pwm output can be seen. 1 Hz frequency in time domain is T=1/f > T=1/1 Hz > T=1 s. So 1 Hz frequency translates to 1 s and my duty cycle is 50% so the led at PB6 pin will blink at half a second rate.

How to Generate Desired/Specific PWM Frequency? Formula derivation and Calculations.

Formula for calculating values for pwm generating is not very complex, it only requires in depth knowledge of the stm32f103 clock, timer structure and timer registers. I divided the formula and method in steps and it is very easy know to calculate the values. Below on right side formula for calculating the value’s for generating specific pwm signal is given and on left side the generic terms used in the formula with their definition/meaning are given.

Timer Tick Frequency

Timer tick frequency is the frequency at which the timer is completing its one instruction cycle.

Counter Frequency

Counter Frequency is the frequency at which we want our timer tick counter to increment.

Stm32f103 Pwm(Pulse Width Modulation) frequency calculation formula

Pwm Resolution

Pwm resolution is number of Pwm steps required to generate a required counter frequency. Usually we use an arbitrary number here and then adjust it according to our need. Pwm resolution must be in between 0-65535 since this value is stored in 16-bit register and maximum 16-bit count is 65535.

Stm32f103 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.

Note: Pwm Resolution and Timer Prescaller are 16-bit registers their value must not exceed 65535.

Now looking at the final formula we need two things in it. Timer Prescaller Value and Pwm Resolutin(Steps). You can assign Timer Prescaller Value or Pwm Resolution(Steps) a fixed value and calculate the other perimeter.

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. If not then take a simple tutorial

Getting started with stmcube-mx keil MDK-ARM v5

Stm32f103 timer 4 configuration using input HSI Clock

Stm32f103c8t6 has 4, 16 bit timers, Timer 1,2,3 and 4. 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. So its good to use them. I am using Timer 4 in the project/tutorial.
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. Channel 1 corresponds to PB6 of stm32f103 microcontroller. The settings diagram is given on the right side.

Stm32f103 timer input clock configuration

I am using internal HSI(High Speed Internal) oscillator/clock store. After dividing the clock with prescallers at different stages the final clock that is supplied to timer 4 is 0.0625MHz, Translating 0.0625Mhz to hz is 62500Hz. So the final timer input frequency is 62500 Hz.

Calculating Values for 1Hz frequency and 50% duty cycle pwm signal output

In the final timer settings it’s time to input the Counter Period/Pwm Resolution(Steps), Prescaler value and Pulse required. Pulse is the duty cycle required and in our case its 50%. Lets Solve the upper formula according to the pwm calculation formula’s given above.
Given values:
Timer Input Clock = 0.0625Mhz or 62500Hz
Required Frequency = 1 Hz (In Time Domain 1 second)
Counter Period/Pwm Resolution(Steps) = 3906 (I picked a random value)

Counter Frequency= frequency required * Counter Period
Counter Frequency= 1Hz * 3906 =3906 Hz

Timer Prescaller value=( Timer Input Clock/Counter Frequency)-1
Timer Prescaller value=(62500 Hz / 3906 Hz) – 1 = 15

Now we have both the value’s Timer Presaller value, Counter Period/Pwm Resolution(Steps) and also they are in 16-bit range. Now input the values in the timer 4 configuration. I selected the counter to be in UP mode(Count for 0 to 3906). Pulse is the duty cycle in our case its 50% so 3906*50% > 3906*0.5 = 1953.

Stm32f103 timer 4 pwm settings

Next advance tutorial on Variable Pwm(Pulse Width Modulation) Output with Stm32f103 microcontroller using stm32cubemx and keil uvision ide. Click the below button to move to tutorial.

Stm32f103 Variable Pwm output using internal timers

Download the Project code. Folder contains the stmcubemx project file and keil Mdk-Arm v5 project files. Please give us your feed back on the project.