c - PIC32 UART 初始化后发送垃圾字符

Question

我正在编写代码来配置 pic32 系列设备上的串行端口。初始化似乎在大部分情况下都有效，但我得到的是垃圾数据，而不是我写入的前 6 个字符。然而，我注意到，如果我在初始化函数末尾添加任意长的等待，这种情况就会消失。在初始化结束时是否需要等待一些寄存器标志？我的初始化代码如下。如果有帮助，我将根据 pic32 reference manual 中的 UART 部分进行此初始化。 。我还为我的传输功能添加了下面的代码。我预期的输出字符串是“Hello from the bootloader code.\r\n”，但我得到的实际字节是:

00000000  00 00 aa b1 b1 bd 81 66  72 6f 6d 20 74 68 65 20  |.......from the |
00000010  62 6f 6f 74 6c 6f 61 64  65 72 20 63 6f 64 65 2e  |bootloader code.|
00000020  0d 0a


void initializeUART2()
{
    uint32 counter;
    initialized = TRUE;
    U2MODE = 0;
    U2STA = 0;
    U2BRG = 0;

    IEC1bits.U2TXIE = 0;
    IEC1bits.U2RXIE = 0;
    IEC1bits.U2EIE = 0;

    //disable UART transmission before config
    U2STA &= ~UART_TRANSMIT_ENABLED_STATUS_FLAG;

    //disable UART before config
    U2MODE &= ~UART_ENABLED_MODE_FLAG;

    RS232_RS485_TRIS=0; //set to output
    RS232_RS485=0; //select RS-232 mode on MAX3161

    //set baudrate BAUDRATE = CLOCK_FREQUENCY/(16*(U2BRG + 1))
    //solve for U2BRG value
    U2BRG = (UINT16)(((PERIPHERAL_CLOCK_FREQUENCY/UART2_BAUDRATE)/16)-1);

    //set mode to 8 bit no parity
    U2MODE &= ~UART_PARITY_DATA_MODE_BITS;

    //set number of stop bits to 1
    U2MODE &= ~UART_EXTRA_STOP_MODE_BIT_FLAG;

    //enable the UART port
    U2MODE |= UART_ENABLED_MODE_FLAG;

    //enable serial transmission
    U2STA |= UART_TRANSMIT_ENABLED_STATUS_FLAG;

    //without this loop, I get garbage in first 6 bytes of my first message
    counter = 1000;
    while(counter--);
}

void putUART2(uint32 value)
{
    if(!initialized)
    {
        initializeUART2();
    }

    //make sure value is in range of writable values
    value &= UINT32_MASK(8);

    //clear transmit interrupt flag
    IFS1bits.U2TXIF = 0;

    //wait for the transmit buffer to be empty
    while((U2STA & UART_TRANSMIT_STATUS_FLAG) == 0);

    //set the data byte to be written in the write register
    //also starts transmission
    U2TXREG = value;

    //wait for the transmit buffer to be empty
    //both of these waits are necessary to avoid missing bytes
    while((U2STA & UART_TRANSMIT_STATUS_FLAG) == 0);
}

Answer 1

MAX3161切换到 RS232 模式后至少需要 100 ns 才能稳定。

此外，这些行:

RS232_RS485_TRIS=0; //set to output
RS232_RS485=0; //select RS-232 mode on MAX3161

应该颠倒；设置输出，然后设置方向寄存器以避免出现故障。