101 lines
3.9 KiB
Plaintext
101 lines
3.9 KiB
Plaintext
/**
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@page TIM_PrescalerSelection TIM PWM Output example
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@verbatim
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******************** (C) COPYRIGHT 2017 STMicroelectronics *******************
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* @file TIM/TIM_PrescalerSelection/readme.txt
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* @author MCD Application Team
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* @brief Description of the PWM signals generation using TIM3
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******************************************************************************
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* @attention
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*
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* Copyright (c) 2017 STMicroelectronics.
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* All rights reserved.
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*
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* This software is licensed under terms that can be found in the LICENSE file
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* in the root directory of this software component.
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* If no LICENSE file comes with this software, it is provided AS-IS.
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*
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******************************************************************************
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@endverbatim
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@par Example Description
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This example shows how to configure the TIM peripheral in PWM (Pulse Width Modulation)
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mode with clock prescaler selection feature activated using __HAL_RCC_TIMCLKPRESCALER()
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which allow to double the output frequency.
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SystemCoreClock is set to 180 MHz for STM32F4xx Devices.
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In this example TIM3 input clock (TIM3CLK) is set to 4 * APB1 clock (PCLK1), since
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Timer clock prescalers selection activated (TIMPRE bit from RCC_DCKCFGR register is set).
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TIM3CLK = 4 * PCLK1
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PCLK1 = HCLK / 4
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=> TIM3CLK = HCLK = SystemCoreClock
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For TIM3CLK equal to SystemCoreClock and prescaler equal to (5 - 1), TIM3 counter clock
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is computed as follows:
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TIM3 counter clock = TIM3CLK / (Prescaler + 1)
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= SystemCoreClock / (Prescaler + 1)
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= 36MHz
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For ARR equal to (1800 - 1), the TIM3 output clock is computed as follows:
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TIM3 output clock = TIM3 counter clock / (ARR + 1)
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= 20KHZ
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The TIM3 CCR1 register value is equal to 900, so the TIM3 Channel 1 generates a
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PWM signal with a frequency equal to 20 KHz and a duty cycle equal to 50%:
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TIM3 Channel1 duty cycle = (TIM3_CCR1/ TIM3_ARR + 1)* 100 = 50%
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The PWM waveforms can be displayed using an oscilloscope.
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@note Care must be taken when using HAL_Delay(), this function provides accurate delay (in milliseconds)
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based on variable incremented in SysTick ISR. This implies that if HAL_Delay() is called from
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a peripheral ISR process, then the SysTick interrupt must have higher priority (numerically lower)
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than the peripheral interrupt. Otherwise the caller ISR process will be blocked.
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To change the SysTick interrupt priority you have to use HAL_NVIC_SetPriority() function.
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@note The application need to ensure that the SysTick time base is always set to 1 millisecond
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to have correct HAL operation.
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@par Keywords
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Timers, PWM, Prescaler, Duty Cycle, Waveform, Oscilloscope, Output, Signal
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@par Directory contents
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- TIM/TIM_PrescalerSelection/Inc/stm32f4xx_hal_conf.h HAL configuration file
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- TIM/TIM_PrescalerSelection/Inc/stm32f4xx_it.h Interrupt handlers header file
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- TIM/TIM_PrescalerSelection/Inc/main.h Header for main.c module
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- TIM/TIM_PrescalerSelection/Src/stm32f4xx_it.c Interrupt handlers
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- TIM/TIM_PrescalerSelection/Src/main.c Main program
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- TIM/TIM_PrescalerSelection/Src/stm32f4xx_hal_msp.c HAL MSP file
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- TIM/TIM_PrescalerSelection/Src/system_stm32f4xx.c STM32F4xx system source file
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@par Hardware and Software environment
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- This example runs on STM32F446xx devices.
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- This example has been tested with STMicroelectronics STM32446E-EVAL
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board and can be easily tailored to any other supported device
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and development board.
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- STM32446E-EVAL Set-up
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Connect the following pins to an oscilloscope to monitor the different waveforms:
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- TIM3_CH1 : PB.04
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@par How to use it ?
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In order to make the program work, you must do the following :
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- Open your preferred toolchain
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- Rebuild all files and load your image into target memory
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- Run the example
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*/
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