最近有项目需要用到STM32F103RCT6的USART1,UART4,UART5。其中USART1和UART4采用DMA方式收发且都能正常工作，唯独这个UART5死活就是能收不能发。而更诡异的是总共焊了5块样板，相同的烧录文件其中有2块UART5可以正常收发另外3块UART5能收不能发。进一步查找原因发现将2块正常的样板和3块不正常的样板交换单片机IC后，发现问题出在单片机IC上，2台正常的样板现在不正常了，而换了IC的2块原来异常的板也正常了。
以下是我的初始化源代码：

1. 
   
2. void UART45_Init(void)
   
3. {
   
4.         //GPIO端口设置
   
5.         GPIO_InitTypeDef GPIO_InitStructure;
   
6.         USART_InitTypeDef USART_InitStructure;
   
7.         DMA_InitTypeDef DMA_InitStructure;
   
8.         RCC_AHBPeriphClockCmd(RCC_AHBPeriph_DMA2, ENABLE);
   
9. 
   
10.         RCC_APB1PeriphClockCmd(RCC_APB1Periph_UART4|RCC_APB1Periph_UART5, ENABLE);
    
11. 
    
12.         USART_DeInit(UART4);
    
13.          //UART45_TX
    
14.     GPIO_InitStructure.GPIO_Pin = GPIO_Pin_10|GPIO_Pin_12;
    
15.     GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
    
16.     GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF_PP;
    
17.     GPIO_Init(GPIOC, &GPIO_InitStructure);
    
18. 
    
19.     //UART4_RX
    
20.     GPIO_InitStructure.GPIO_Pin = GPIO_Pin_11;
    
21.     GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IN_FLOATING;
    
22.     GPIO_Init(GPIOC, &GPIO_InitStructure);
    
23.     //UART5_RX
    
24.         GPIO_InitStructure.GPIO_Pin = GPIO_Pin_2;
    
25.         GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IN_FLOATING;
    
26.         GPIO_Init(GPIOD, &GPIO_InitStructure);
    
27.    //USART 初始化设置
    
28. 
    
29.         USART_InitStructure.USART_BaudRate = 9600;
    
30.         USART_InitStructure.USART_WordLength = USART_WordLength_8b;
    
31.         USART_InitStructure.USART_StopBits = USART_StopBits_1;
    
32.         USART_InitStructure.USART_Parity = USART_Parity_No;
    
33.         USART_InitStructure.USART_HardwareFlowControl = USART_HardwareFlowControl_None;
    
34.         USART_InitStructure.USART_Mode = USART_Mode_Rx | USART_Mode_Tx;
    
35. 
    
36.     USART_Init(UART4, &USART_InitStructure);
    
37.     USART_Init(UART5, &USART_InitStructure);
    
38.     USART_ITConfig(UART4, USART_IT_IDLE, ENABLE);
    
39.     USART_ITConfig(UART5, USART_IT_IDLE, ENABLE);
    
40.     USART_ITConfig(UART5, USART_IT_RXNE, ENABLE);
    
41.     USART_Cmd(UART4, ENABLE);
    
42.     USART_Cmd(UART5, ENABLE);
    
43. 
    
44.         DMA_DeInit(DMA2_Channel3);
    
45.         DMA_InitStructure.DMA_PeripheralBaseAddr = (uint32_t)&UART4->DR;
    
46.         DMA_InitStructure.DMA_MemoryBaseAddr = (uint32_t)(u4rxd_array);
    
47.         DMA_InitStructure.DMA_DIR = DMA_DIR_PeripheralSRC;
    
48.         DMA_InitStructure.DMA_BufferSize = sizeof(u4rxd_array);
    
49.         DMA_InitStructure.DMA_PeripheralInc = DMA_PeripheralInc_Disable;
    
50.         DMA_InitStructure.DMA_MemoryInc = DMA_MemoryInc_Enable;
    
51.         DMA_InitStructure.DMA_PeripheralDataSize = DMA_PeripheralDataSize_Byte;
    
52.         DMA_InitStructure.DMA_MemoryDataSize = DMA_MemoryDataSize_Byte;
    
53.         DMA_InitStructure.DMA_Mode = DMA_Mode_Normal;
    
54.         DMA_InitStructure.DMA_Priority = DMA_Priority_Medium;
    
55.         DMA_InitStructure.DMA_M2M = DMA_M2M_Disable;
    
56.         DMA_Init(DMA2_Channel3, &DMA_InitStructure);
    
57. 
    
58.         DMA_ITConfig(DMA2_Channel3, DMA_IT_TC, ENABLE);
    
59. 
    
60.         USART_DMACmd(UART4, USART_DMAReq_Rx, ENABLE);
    
61.         DMA_Cmd (DMA2_Channel3,ENABLE);
    
62. 
    
63.     DMA_DeInit(DMA2_Channel5);
    
64.         DMA_InitStructure.DMA_PeripheralBaseAddr = (uint32_t)&UART4->DR;
    
65.         DMA_InitStructure.DMA_MemoryBaseAddr = (uint32_t)(u4txd_array);
    
66.         DMA_InitStructure.DMA_DIR = DMA_DIR_PeripheralDST;
    
67.         DMA_InitStructure.DMA_BufferSize = 0;
    
68.         DMA_InitStructure.DMA_PeripheralInc = DMA_PeripheralInc_Disable;
    
69.         DMA_InitStructure.DMA_MemoryInc = DMA_MemoryInc_Enable;
    
70.         DMA_InitStructure.DMA_PeripheralDataSize = DMA_PeripheralDataSize_Byte;
    
71.         DMA_InitStructure.DMA_MemoryDataSize = DMA_MemoryDataSize_Byte;
    
72.         DMA_InitStructure.DMA_Mode = DMA_Mode_Normal;
    
73.         DMA_InitStructure.DMA_Priority = DMA_Priority_Medium;
    
74.         DMA_InitStructure.DMA_M2M = DMA_M2M_Disable;
    
75.         DMA_Init(DMA2_Channel5, &DMA_InitStructure);
    
76. 
    
77.         DMA_ITConfig(DMA2_Channel5, DMA_IT_TC, DISABLE);
    
78. 
    
79.         USART_DMACmd(UART4, USART_DMAReq_Tx, ENABLE);
    
80.         DMA_Cmd (DMA2_Channel5,DISABLE);
    
81. }
    

复制代码

debug发现不正常的样板向UART5->DR写数据其值不会发生变化，请高人指点一下@香水城

这就奇怪了，既然部分产品可以，说明软件大体上没问题。最好单独测试串口5，先测试IO引脚是否输出，确定硬件连接通过，再用单独测试串口5 的软件，保证配置寄存器内容正确

uar5是直接连接到串口吗？还是过了232这类芯片。建议检测IO波形，如果波形正常，说明是后面的电路的问题，再一步一步的排查，可能是电平转换芯片那边有虚焊或者漏焊的。

话说会不是买到炸弹货了  有的芯片好 有的芯片坏的

没办法最后还是放弃了UART5改用USART3就没有问题了