STM32F0紅外發(fā)射功能的應(yīng)用

久聞STM32F0系列內(nèi)置IR_OUT紅外發(fā)射功能，此次有幸得到社區(qū)贈送STM32F0308-DISCOVERY，終于有機會動手體會。
在許多應(yīng)用場合需要紅外發(fā)射管連續(xù)發(fā)送經(jīng)過調(diào)制的38KHZ脈沖信號，經(jīng)過接收頭接收后送信號處理電路來判斷其間有否物體經(jīng)過。以往使用單片機來處理需要先從IO口產(chǎn)生38KHZ的PWM信號，再通過定時器中斷來控制PWM信號的開啟和關(guān)斷。本例中定時器需要每500微秒中斷一次來執(zhí)行該任務(wù)，當CPU還有其他更重要的任務(wù)要處理日就顯得有些緊張。


圖1

STM32F0系列的一個特色是增加了IR_OUT功能，它在內(nèi)部把TIM17-CCR1和TIM16-CCR1經(jīng)過與非門從IR_OUT輸出（圖1），這樣，我們只要配置好TIM16和TIM17的PWM參數(shù)，并把復用功能分配給IR_OUT，在這里是PB9-AF0,就可以完全不占用CPU時間而達到所需功能。此例中TIM17負責IR的載頻，TIM16負責IR的調(diào)制，我們把TIM17的PWM配置成38KHZ占空比75%，TIM16的PWM配置成1KHZ占空比50%。由于紅外發(fā)射管是在PWM低電平時導通，因此38K載頻信號的占空比為25%。運行結(jié)果見圖2和圖3.。


圖2 調(diào)制后的信號波形



圖3波形展開

附代碼：

#include "stm32f0xx.h"
uint16_t TimerPeriod16 = 0,Channel1Pulse16 =0,TimerPeriod17 = 0,Channel1Pulse17 =0;;
void GPIO_Config(void);
void TIM_Config(void);
//----------------------------------------------------------------------------
int main(void)
{ GPIO_Config();
TIM_Config();
while (1)
{}
}
//----------------------------------------------------------------------------
void GPIO_Config(void)
{ PIO_InitTypeDef GPIO_InitStructure;
RCC_AHBPeriphClockCmd( RCC_AHBPeriph_GPIOB, ENABLE);
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_9 ;
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF;
GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;
GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_UP ;
GPIO_Init(GPIOB, &GPIO_InitStructure);
GPIO_PinAFConfig(GPIOB, GPIO_PinSource9, GPIO_AF_0);
}
//--------------------------------------------------------------------------
void TIM_Config(void)
{TIM_TimeBaseInitTypeDef TIM_TimeBaseStructure;
TIM_OCInitTypeDef TIM_OCInitStructure;
TimerPeriod16 = (SystemCoreClock /1000) - 1;
Channel1Pulse16 = (uint16_t) (((uint32_t) 5 * (TimerPeriod16 - 1)) / 10);
TimerPeriod17 = (SystemCoreClock /38000) - 1;
Channel1Pulse17 = (uint16_t) (((uint32_t) 75 * (TimerPeriod17 - 1)) / 100);
RCC_APB2PeriphClockCmd(RCC_APB2Periph_TIM16|RCC_APB2Periph_TIM17, ENABLE);
TIM_TimeBaseStructure.TIM_Prescaler = 0;
TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;
TIM_TimeBaseStructure.TIM_Period = TimerPeriod16;
TIM_TimeBaseStructure.TIM_ClockDivision = 0;
TIM_TimeBaseStructure.TIM_RepetitionCounter = 0;
TIM_TimeBaseInit(TIM16, &TIM_TimeBaseStructure);

TIM_OCInitStructure.TIM_OCMode = TIM_OCMode_PWM1;
TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;
TIM_OCInitStructure.TIM_OutputNState = TIM_OutputNState_Enable;
TIM_OCInitStructure.TIM_OCPolarity = TIM_OCPolarity_Low;
TIM_OCInitStructure.TIM_OCNPolarity = TIM_OCNPolarity_High;
TIM_OCInitStructure.TIM_OCIdleState = TIM_OCIdleState_Set;
TIM_OCInitStructure.TIM_OCNIdleState = TIM_OCIdleState_Reset;

TIM_OCInitStructure.TIM_Pulse = Channel1Pulse16;
TIM_OC1Init(TIM16, &TIM_OCInitStructure);
TIM_Cmd(TIM16, ENABLE);
TIM_CtrlPWMOutputs(TIM16, ENABLE);

TIM_TimeBaseStructure.TIM_Prescaler = 0;
TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;
TIM_TimeBaseStructure.TIM_Period = TimerPeriod17;
TIM_TimeBaseStructure.TIM_ClockDivision = 0;
TIM_TimeBaseStructure.TIM_RepetitionCounter = 0;
TIM_TimeBaseInit(TIM17, &TIM_TimeBaseStructure);

TIM_OCInitStructure.TIM_OCMode = TIM_OCMode_PWM1;
TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;
TIM_OCInitStructure.TIM_OutputNState = TIM_OutputNState_Enable;
TIM_OCInitStructure.TIM_OCPolarity = TIM_OCPolarity_Low;
TIM_OCInitStructure.TIM_OCNPolarity = TIM_OCNPolarity_High;
TIM_OCInitStructure.TIM_OCIdleState = TIM_OCIdleState_Set;
TIM_OCInitStructure.TIM_OCNIdleState = TIM_OCIdleState_Reset;

TIM_OCInitStructure.TIM_Pulse = Channel1Pulse17;
TIM_OC1Init(TIM17, &TIM_OCInitStructure);
TIM_Cmd(TIM17, ENABLE);
TIM_CtrlPWMOutputs(TIM17, ENABLE);
}