STM32F030R8 RS485 半双工不传输

Question

我正在使用 STM32F030R8 执行连接到 AD3485 的 RS485 通信。到目前为止，我已经能够让它传输得很好，但是当我设置一个中断处理程序时，似乎中断是由我的芯片自己的传输触发的，并停止了所有进一步的传输。

我是否错过了在某处设置或清除标志？我是否遗漏了 RS485 初始化步骤中的某些内容？当我的传输不可避免地触发中断请求时，我是否应该清除标志？

下面我包含了一个非常精简但完整的代码版本，我正在使用它来传输数据，以及我看到的从我拥有的 RS485 芯片中捕获的数据连接到引脚 A9 A10 和 A12。

代码如下：

#include "stm32f0xx_conf.h"
#include <stm32f0xx_gpio.h>
#include <stm32f0xx_rcc.h>
#include <stm32f0xx_usart.h>

void SysTick_Handler(void) {

    while (USART_GetFlagStatus(USART1, USART_FLAG_TXE) == RESET);
    USART_SendData(USART1, 0xAC);
    while(USART_GetFlagStatus(USART1, USART_FLAG_TC) == RESET);
    USART_SendData(USART1, 0x44);
    while(USART_GetFlagStatus(USART1, USART_FLAG_TC) == RESET);
    USART_SendData(USART1, 0x04);
    while(USART_GetFlagStatus(USART1, USART_FLAG_TC) == RESET);
    USART_SendData(USART1, 0x53);
    while(USART_GetFlagStatus(USART1, USART_FLAG_TC) == RESET);

}

void RS485_Init(){
    GPIO_InitTypeDef GPIO_InitStruct;
    USART_InitTypeDef USART_InitStruct;
    NVIC_InitTypeDef NVIC_InitStruct;

    RCC_APB2PeriphClockCmd(RCC_APB2Periph_USART1, ENABLE);
    RCC_AHBPeriphClockCmd(RCC_AHBPeriph_GPIOA, ENABLE);

    GPIO_InitStruct.GPIO_Pin = GPIO_Pin_9 | GPIO_Pin_10 | GPIO_Pin_12; // Pins 9 (TX) 10 (RX) 12 (DE) are used
    GPIO_InitStruct.GPIO_Mode = GPIO_Mode_AF; // the pins are configured as alternate function so the USART peripheral has access to them
    GPIO_InitStruct.GPIO_Speed = GPIO_Speed_50MHz; // this defines the IO speed and has nothing to do with the baudrate!
    GPIO_InitStruct.GPIO_OType = GPIO_OType_PP; // this defines the output type as push pull mode (as opposed to open drain)
    GPIO_InitStruct.GPIO_PuPd = GPIO_PuPd_UP; // this activates the pullup resistors on the IO pins
    GPIO_Init(GPIOA, &GPIO_InitStruct);

    GPIO_PinAFConfig(GPIOA, GPIO_PinSource9, GPIO_AF_1); //
    GPIO_PinAFConfig(GPIOA, GPIO_PinSource10, GPIO_AF_1);
    GPIO_PinAFConfig(GPIOA, GPIO_PinSource12, GPIO_AF_1);

    USART_InitStruct.USART_BaudRate = 38400 ; // the baudrate is set to the value we passed into this init function
    USART_InitStruct.USART_WordLength = USART_WordLength_8b; // we want the data frame size to be 8 bits (standard)
    USART_InitStruct.USART_StopBits = USART_StopBits_1; // we want 1 stop bit (standard)
    USART_InitStruct.USART_Parity = USART_Parity_No; // we don't want a parity bit (standard)
    USART_InitStruct.USART_HardwareFlowControl = USART_HardwareFlowControl_None; // we don't want flow control (standard)
    USART_InitStruct.USART_Mode = USART_Mode_Tx | USART_Mode_Rx; // we want to enable the transmitter and the receiver
    USART_Init(USART1, &USART_InitStruct);

    USART_HalfDuplexCmd(USART1, ENABLE);
    USART_DECmd(USART1, ENABLE);
    USART_ITConfig(USART1, USART_IT_TXE, DISABLE);
    USART_ITConfig(USART1, USART_IT_RXNE, ENABLE);
    USART_SetDEAssertionTime(USART1, 0x4E2);
    USART_SetDEDeassertionTime(USART1, 0x4E2);
    USART_DEPolarityConfig(USART1, USART_DEPolarity_High);

    NVIC_InitStruct.NVIC_IRQChannel = USART1_IRQn;
    NVIC_InitStruct.NVIC_IRQChannelPriority = 0;
    NVIC_InitStruct.NVIC_IRQChannelCmd = ENABLE;
    NVIC_Init(&NVIC_InitStruct); //When I comment this out, I'm able to transmit normally, but without an ISR receiving bytes will be difficult

    USART_Cmd(USART1, ENABLE);

}

//This function handles USART1 global interrupt request.
void USART1_IRQHandler(void)
{

    if(USART_GetITStatus(USART1, USART_IT_RXNE) != RESET){
        unsigned char USART_Temp_Byte;
        USART_ClearITPendingBit(USART1, USART_IT_RXNE);
        USART_Temp_Byte = (unsigned char) USART_ReceiveData(USART1); //receive a char
    }

}

int main(void)
{
    RS485_Init();
    SysTick_Config(SystemCoreClock/1000);
    while(1);
}

下面是启用中断时的捕获（第一次捕获），以及注释掉 NVIC_Init(&NVIC_InitStruct) 时的捕获；并且没有 ISR 触发：

Answer 1

这是half/full双工通信方式的核心原则之一。 RS485 是一种物理层标准，允许发送器接收自己的数据。这对于其他标准（软件层）很有用，例如 J1708。由于没有单主多从的硬性要求，每个节点都可以发起一次通信。如果两个模块同时开始通话，则需要有一种方案来检测和处理总线contentions/collisions。使用 RS485，您有一个显性（驱动）状态和一个隐性（non-driven）状态。当发射器开始传输时，您会监控接收到的内容是否与发送的内容相匹配，如果不匹配，很可能是另一台设备同时尝试传输。这是可行的，因为当您从显性状态切换到隐性状态时，总线将 return 变为隐性状态（无冲突），或者由于另一个接收器保持线路（冲突）而保持显性状态。发生这种情况时，您将停止任何进一步的传输并开始接收或监视总线是否处于空闲状态。大多数协议，如 J1708，使用基于您的地址的伪随机生成器来计算重试延迟，从而防止相同的两个模块不断发生冲突。长话短说：您正在接收您传输的内容这一事实是一件好事。我建议您使用中断来比较刚刚传输的字节和刚刚接收的字节，如果它们匹配，则发送下一个字节，否则终止并在检测到下一个空闲状态后重试。由于它是相同的中断例程，您需要设置一个标志来指示您何时传输并控制中断逻辑来处理比较（Tx 部分）或处理正常接收（Rx 部分）

Answer 2

我将此答案添加为更新，以让半双工通信与此特定芯片一起工作。通过这种配置，我既可以发送也可以接收。特别感谢 Joe Thomas 让我走上正轨。

#include "stm32f0xx_conf.h"
#include <stm32f0xx_gpio.h>
#include <stm32f0xx_rcc.h>
#include <stm32f0xx_usart.h>

void Transmit(void){

    USART_Cmd(USART1, DISABLE);
    USART_DECmd(USART1, ENABLE);
    USART_ITConfig(USART1, USART_IT_TXE, ENABLE);
    USART_ITConfig(USART1, USART_IT_RXNE, DISABLE);
    USART_Cmd(USART1, ENABLE);

    while (USART_GetFlagStatus(USART1, USART_FLAG_TXE) == RESET);

    USART_SendData(USART1, 0xAC);
    while(USART_GetFlagStatus(USART1, USART_FLAG_TC) == RESET);
    while (USART_GetFlagStatus(USART1, USART_FLAG_TXE) == RESET);

    USART_SendData(USART1, 0x44);
    while(USART_GetFlagStatus(USART1, USART_FLAG_TC) == RESET);
    while (USART_GetFlagStatus(USART1, USART_FLAG_TXE) == RESET);

    USART_SendData(USART1, 0x04);
    while(USART_GetFlagStatus(USART1, USART_FLAG_TC) == RESET);
    while (USART_GetFlagStatus(USART1, USART_FLAG_TXE) == RESET);

    USART_SendData(USART1, 0x53);
    while(USART_GetFlagStatus(USART1, USART_FLAG_TC) == RESET);
    while (USART_GetFlagStatus(USART1, USART_FLAG_TXE) == RESET);

    USART_Cmd(USART1, DISABLE);
    USART_DECmd(USART1, DISABLE);
    USART_ITConfig(USART1, USART_IT_RXNE, ENABLE);
    USART_ITConfig(USART1, USART_IT_TXE, DISABLE);
    USART_Cmd(USART1, ENABLE);

}

void SysTick_Handler(void) {

}

void RS485_Init(){

    GPIO_InitTypeDef GPIO_InitStruct;
    USART_InitTypeDef USART_InitStruct;
    NVIC_InitTypeDef NVIC_InitStruct;



    RCC_APB2PeriphClockCmd(RCC_APB2Periph_USART1, ENABLE);
    RCC_AHBPeriphClockCmd(RCC_AHBPeriph_GPIOA, ENABLE);

    GPIO_InitStruct.GPIO_Pin = GPIO_Pin_9 | GPIO_Pin_10 | GPIO_Pin_12;
    GPIO_InitStruct.GPIO_Mode = GPIO_Mode_AF;
    GPIO_InitStruct.GPIO_Speed = GPIO_Speed_50MHz;
    GPIO_InitStruct.GPIO_OType = GPIO_OType_PP;
    GPIO_InitStruct.GPIO_PuPd = GPIO_PuPd_UP;
    GPIO_Init(GPIOA, &GPIO_InitStruct);

    GPIO_PinAFConfig(GPIOA, GPIO_PinSource9, GPIO_AF_1);
    GPIO_PinAFConfig(GPIOA, GPIO_PinSource10, GPIO_AF_1);
    GPIO_PinAFConfig(GPIOA, GPIO_PinSource12, GPIO_AF_1);

    USART_DeInit(USART1);
    USART_StructInit(&USART_InitStruct);
    USART_InitStruct.USART_BaudRate = 38400 ;
    USART_InitStruct.USART_WordLength = USART_WordLength_8b;
    USART_InitStruct.USART_StopBits = USART_StopBits_1;
    USART_InitStruct.USART_Parity = USART_Parity_No;
    USART_InitStruct.USART_HardwareFlowControl = USART_HardwareFlowControl_RTS;
    USART_InitStruct.USART_Mode = USART_Mode_Tx | USART_Mode_Rx;
    USART_Init(USART1, &USART_InitStruct);

    USART_HalfDuplexCmd(USART1, DISABLE);
    USART_DECmd(USART1, DISABLE);
    USART_ITConfig(USART1, USART_IT_TXE, DISABLE);
    USART_ITConfig(USART1, USART_IT_RXNE, ENABLE);
    USART_SetDEAssertionTime(USART1, 0x4E2);
    USART_SetDEDeassertionTime(USART1, 0x4E2);
    USART_DEPolarityConfig(USART1, USART_DEPolarity_High);



    NVIC_InitStruct.NVIC_IRQChannel = USART1_IRQn;
    NVIC_InitStruct.NVIC_IRQChannelPriority = 0;
    NVIC_InitStruct.NVIC_IRQChannelCmd = ENABLE;
    NVIC_Init(&NVIC_InitStruct);

    USART_ClearITPendingBit(USART1, USART_IT_RXNE);
    USART_ITConfig(USART1, USART_IT_RXNE, ENABLE);

    USART_Cmd(USART1, ENABLE);

}

void USART1_IRQHandler(void)
{

    if(USART_GetITStatus(USART1, USART_IT_RXNE) != RESET){
        unsigned char USART_Temp_Byte;
        USART_ClearITPendingBit(USART1, USART_IT_RXNE);
        USART_Temp_Byte = (unsigned char) USART_ReceiveData(USART1); //receive a char
        if(0x53 == USART_Temp_Byte){
            Transmit();
        }
    }

}

int main(void)
{
    RS485_Init();
    SysTick_Config(SystemCoreClock/1000);
    while(1){};
}

STM32F030R8 RS485 半双工不传输

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