最近專案中STM32的串列埠資源緊張，於是使用IO口進行模擬串列埠，現進行整理記錄。

1. 實現思路

IO口模擬串列埠的思路也比較簡單，一切按照串列埠協議進行操作即可。

對於傳送，計算好不同波特率對應的延時時間進行資料傳送。

對於接收，稍微複雜。通過外部中斷檢測接收管腳的下降沿，檢測到起始訊號後開啟定時器，定時器按照波特率設定好時間，每隔一段時間進入定時器中斷接收資料，完成一個位元組後關閉定時器。

2. 測試Demo說明

• TXD : PC13
• RXD : PB14
• 波特率：9600 ，1-8-N

3. Demo功能

接收11個數據，然後把接收到的資料傳送出去。

4. 程式實現

#define OI_TXD	PCout(13)
 

#define OI_RXD	PBin(14)

#define BuadRate_9600	100

u8 len = 0;	//接收計數
u8 USART_buf[11];  //接收緩衝區

enum{
	COM_START_BIT,
	COM_D0_BIT,
	COM_D1_BIT,
	COM_D2_BIT,
	COM_D3_BIT,
	COM_D4_BIT,
	COM_D5_BIT,
	COM_D6_BIT,
	COM_D7_BIT,
	COM_STOP_BIT,
};

u8 recvStat = COM_STOP_BIT;
u8 recvData = 0;

void IO_TXD(u8 Data)
 

{
	u8 i = 0;
	OI_TXD = 0;  
	delay_us(BuadRate_9600);
	for(i = 0; i < 8; i++)
	{
		if(Data&0x01)
			OI_TXD = 1;  
		else
			OI_TXD = 0; 	
		
		delay_us(BuadRate_9600);
		Data = Data>>1;
	}
	OI_TXD = 1;
	delay_us(BuadRate_9600);
}
	
void USART_Send(u8 *buf, u8 len)
{
	u8 t;
	for(t = 0; t < len; t++
 
)
	{
		IO_TXD(buf[t]);
	}
}
	
 void IOConfig(void)
 {
	GPIO_InitTypeDef  GPIO_InitStructure;
	NVIC_InitTypeDef NVIC_InitStructure;
 	EXTI_InitTypeDef EXTI_InitStruct;
  RCC_APB2PeriphClockCmd(RCC_APB2Periph_AFIO|RCC_APB2Periph_GPIOB|RCC_APB2Periph_GPIOC, ENABLE);	 //使能PB,PC埠時鐘 
	 
	 //SoftWare Serial TXD
	GPIO_InitStructure.GPIO_Pin = GPIO_Pin_13;	    
  GPIO_InitStructure.GPIO_Mode = GPIO_Mode_Out_PP; 		 //推輓輸出
  GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;		 //IO口速度為50MHz	 
  GPIO_Init(GPIOC, &GPIO_InitStructure);	  				
  GPIO_SetBits(GPIOC,GPIO_Pin_13); 						
	 
	 
	//SoftWare Serial RXD
	GPIO_InitStructure.GPIO_Pin = GPIO_Pin_14;
  GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IPU;
  GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;		
	GPIO_Init(GPIOB, &GPIO_InitStructure);	 

	GPIO_EXTILineConfig(GPIO_PortSourceGPIOB, GPIO_PinSource14);
	EXTI_InitStruct.EXTI_Line = EXTI_Line14;
	EXTI_InitStruct.EXTI_Mode=EXTI_Mode_Interrupt;
	EXTI_InitStruct.EXTI_Trigger=EXTI_Trigger_Falling; //下降沿觸發中斷
	EXTI_InitStruct.EXTI_LineCmd=ENABLE;
	EXTI_Init(&EXTI_InitStruct);


	NVIC_InitStructure.NVIC_IRQChannel= EXTI15_10_IRQn ; 
	NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority=2; 
	NVIC_InitStructure.NVIC_IRQChannelSubPriority =2;  
	NVIC_InitStructure.NVIC_IRQChannelCmd=ENABLE;  
	NVIC_Init(&NVIC_InitStructure);  
	
}
 
void TIM4_Int_Init(u16 arr,u16 psc)
{
  TIM_TimeBaseInitTypeDef  TIM_TimeBaseStructure;
	NVIC_InitTypeDef NVIC_InitStructure;

	RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM4, ENABLE); //時鐘使能
	
	//定時器TIM4初始化
	TIM_TimeBaseStructure.TIM_Period = arr; //設定在下一個更新事件裝入活動的自動重灌載暫存器週期的值	
	TIM_TimeBaseStructure.TIM_Prescaler =psc; //設定用來作為TIMx時鐘頻率除數的預分頻值
	TIM_TimeBaseStructure.TIM_ClockDivision = TIM_CKD_DIV1; //設定時鐘分割:TDTS = Tck_tim
	TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;  //TIM向上計數模式
	TIM_TimeBaseInit(TIM4, &TIM_TimeBaseStructure); //根據指定的引數初始化TIMx的時間基數單位
	TIM_ClearITPendingBit(TIM4, TIM_FLAG_Update);
	TIM_ITConfig(TIM4,TIM_IT_Update,ENABLE ); //使能指定的TIM3中斷,允許更新中斷

	//中斷優先順序NVIC設定
	NVIC_InitStructure.NVIC_IRQChannel = TIM4_IRQn;  //TIM4中斷
	NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 1;  //先佔優先順序1級
	NVIC_InitStructure.NVIC_IRQChannelSubPriority = 1;  //從優先順序1級
	NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE; //IRQ通道被使能
	NVIC_Init(&NVIC_InitStructure);  //初始化NVIC暫存器			 
}
 
 
 int main(void)
 {		
	 NVIC_PriorityGroupConfig(NVIC_PriorityGroup_2);//設定中斷優先順序分組為組2：2位搶佔優先順序，2位響應優先順序
	 delay_init();
	 IOConfig();
  TIM4_Int_Init(107, 71);	 //1M計數頻率
	 
  while(1)
	{
		if(len > 10)
		{
			len = 0;
			USART_Send(USART_buf,11);
		}
	}
}

void EXTI15_10_IRQHandler(void)
{
	if(EXTI_GetFlagStatus(EXTI_Line14) != RESET)
	{
		if(OI_RXD == 0) 
		{
			if(recvStat == COM_STOP_BIT)
			{
				recvStat = COM_START_BIT;
				TIM_Cmd(TIM4, ENABLE);
			}
		}
		EXTI_ClearITPendingBit(EXTI_Line14);
	}
}

void TIM4_IRQHandler(void)
{  
	if(TIM_GetFlagStatus(TIM4, TIM_FLAG_Update) != RESET)
	{
		TIM_ClearITPendingBit(TIM4, TIM_FLAG_Update);	
		 recvStat++;
		if(recvStat == COM_STOP_BIT)
		{
			TIM_Cmd(TIM4, DISABLE);
			USART_buf[len++] = recvData;	
			return;
		}
		if(OI_RXD)
		{
			recvData |= (1 << (recvStat - 1));
		}else{
			recvData &= ~(1 << (recvStat - 1));
		}	
  }		
}

5. Demo下載

Demo工程下載地址github。