STM32CubeF4

/**
  @page TIM_PrescalerSelection TIM Prescaler Selection example

  @verbatim
  ******************** (C) COPYRIGHT 2017 STMicroelectronics *******************
  * @file    TIM/TIM_PrescalerSelection/readme.txt 
  * @author  MCD Application Team
  * @brief   Description of the PWM signals generation using Timer3 Example
  ******************************************************************************
  * @attention
  *
  * Copyright (c) 2017 STMicroelectronics.
  * All rights reserved.
  *
  * This software is licensed under terms that can be found in the LICENSE file
  * in the root directory of this software component.
  * If no LICENSE file comes with this software, it is provided AS-IS.
  *
  ******************************************************************************
   @endverbatim

@par Example Description 

This example shows how to configure the TIM peripheral in PWM (Pulse Width Modulation) 
mode with clock prescaler selection feature activated using __HAL_RCC_TIMCLKPRESCALER()
which allow to double the output frequency.

In this example TIM3 input clock (TIM3CLK) is set to 4 * APB1 clock (PCLK1), since 
Timer clock prescalers selection activated (TIMPRE bit from RCC_DCKCFGR register is set).   
      TIM3CLK = 4 * PCLK1  
      PCLK1 = HCLK / 4 
      => TIM3CLK = HCLK = SystemCoreClock
          
SystemCoreClock is set to 180 MHz for STM32F4xx Devices.

For TIM3CLK equal to SystemCoreClock and prescaler equal to (5 - 1), TIM3 counter clock 
is computed as follows:
      TIM3 counter clock = TIM3CLK / (Prescaler + 1)
                         = SystemCoreClock / (Prescaler + 1)
                         = 36MHz

For ARR equal to (1800 - 1), the TIM3 output clock is computed as follows:
      TIM3 output clock = TIM3 counter clock / (ARR + 1)
                        = 20KHZ
                         
The TIM3 CCR1 register value is equal to 900, so the TIM3 Channel 1 generates a 
PWM signal with a frequency equal to 20 KHz and a duty cycle equal to 50%:

    TIM3 Channel1 duty cycle = (TIM3_CCR1/ TIM3_ARR + 1)* 100 = 50%

The PWM waveform can be displayed using an oscilloscope.


@note Care must be taken when using HAL_Delay(), this function provides accurate delay (in milliseconds)
      based on variable incremented in SysTick ISR. This implies that if HAL_Delay() is called from
      a peripheral ISR process, then the SysTick interrupt must have higher priority (numerically lower)
      than the peripheral interrupt. Otherwise the caller ISR process will be blocked.
      To change the SysTick interrupt priority you have to use HAL_NVIC_SetPriority() function.
      
@note The application needs to ensure that the SysTick time base is always set to 1 millisecond
      to have correct HAL operation.

@par Keywords

Timers, PWM, Prescaler, Duty Cycle, Waveform, Oscilloscope, Output, Signal

@par Directory contents 

  - TIM/TIM_PrescalerSelection/Inc/stm32f4xx_hal_conf.h     HAL configuration file
  - TIM/TIM_PrescalerSelection/Inc/stm32f4xx_it.h           Interrupt handlers header file
  - TIM/TIM_PrescalerSelection/Inc/main.h                   Main program header file  
  - TIM/TIM_PrescalerSelection/Src/stm32f4xx_it.c           Interrupt handlers
  - TIM/TIM_PrescalerSelection/Src/main.c                   Main program
  - TIM/TIM_PrescalerSelection/Src/stm32f4xx_hal_msp.c      HAL MSP module
  - TIM/TIM_PrescalerSelection/Src/system_stm32f4xx.c       STM32F4xx system clock configuration file


@par Hardware and Software environment 

  - This example runs on STM32F429xx/STM32F439xx devices.
    
  - This example has been tested with STMicroelectronics STM324x9I-EVAL RevB(STM32F42xxx/43xxx devices) 
    evaluation boards and can be easily tailored to any other supported device and development board

  - STM324x9I-EVAL RevB Set-up 
    - Connect the following pins to an oscilloscope to monitor the different 
      waveforms:
        - PC.06: (TIM3_CH1)


@par How to use it ? 

In order to make the program work, you must do the following :
 - Open your preferred toolchain 
 - Rebuild all files and load your image into target memory
 - Run the example


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