基于MM32F3277G9P写出一个程序，其功能是：当在串口发送11111111时，实现利用HC-SR04的超声波测距功能，并显示在MAX7219数码管上

好的，根据您的要求，我为您编写了以下代码：

#include <stdio.h>
#include "MM32F3277.h"

#define TRIG_Pin GPIO_Pin_12
#define ECHO_Pin GPIO_Pin_13
#define MAX7219_DIN_Pin GPIO_Pin_1
#define MAX7219_CS_Pin GPIO_Pin_2
#define MAX7219_CLK_Pin GPIO_Pin_3

void delay_us(uint32_t us)
{
    uint32_t i;
    for(i=0;i<us*8;i++);
}

void delay_ms(uint32_t ms)
{
    uint32_t i;
    for(i=0;i<ms*8000;i++);
}

void GPIO_Config(void)
{
    GPIO_InitTypeDef GPIO_InitStructure;

    RCC_AHBPeriphClockCmd(RCC_AHBPeriph_GPIOA, ENABLE);

    GPIO_InitStructure.GPIO_Pin = TRIG_Pin;
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_OUT;
    GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
    GPIO_Init(GPIOA, &GPIO_InitStructure);

    GPIO_InitStructure.GPIO_Pin = ECHO_Pin;
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IN;
    GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
    GPIO_Init(GPIOA, &GPIO_InitStructure);

    RCC_AHBPeriphClockCmd(RCC_AHBPeriph_GPIOB, ENABLE);

    GPIO_InitStructure.GPIO_Pin = MAX7219_DIN_Pin | MAX7219_CLK_Pin | MAX7219_CS_Pin;
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_OUT;
    GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
    GPIO_Init(GPIOB, &GPIO_InitStructure);
}

void USART_Config(void)
{
    USART_InitTypeDef USART_InitStructure;

    RCC_APB2PeriphClockCmd(RCC_APB2Periph_USART1, ENABLE);

    USART_InitStructure.USART_BaudRate = 115200;
    USART_InitStructure.USART_WordLength = USART_WordLength_8b;
    USART_InitStructure.USART_StopBits = USART_StopBits_1;
    USART_InitStructure.USART_Parity = USART_Parity_No;
    USART_InitStructure.USART_HardwareFlowControl = USART_HardwareFlowControl_None;
    USART_InitStructure.USART_Mode = USART_Mode_Rx;

    USART_Init(USART1, &USART_InitStructure);

    USART_Cmd(USART1, ENABLE);
}

void MAX7219_WriteByte(uint8_t data)
{
    uint8_t i;

    GPIO_ResetBits(GPIOB, MAX7219_CS_Pin);

    for(i=8;i>0;i--)
    {
        GPIO_ResetBits(GPIOB, MAX7219_CLK_Pin);
        GPIO_WriteBit(GPIOB, MAX7219_DIN_Pin, (BitAction)(data>>(i-1)&0x01));
        GPIO_SetBits(GPIOB, MAX7219_CLK_Pin);
    }

    GPIO_SetBits(GPIOB, MAX7219_CS_Pin);
}

void MAX7219_Init(void)
{
    MAX7219_WriteByte(0x0C);
    MAX7219_WriteByte(0x01);
    MAX7219_WriteByte(0x0F);
    MAX7219_WriteByte(0x00);
}

void MAX7219_Display(uint16_t num)
{
    uint16_t digit;
    uint8_t i;

    if(num == 0)
    {
        MAX7219_WriteByte(0x01);
        MAX7219_WriteByte(0x00);
        return;
    }

    for(i=1;i<=8;i++)
    {
        digit = num % 10;
        MAX7219_WriteByte(i);
        MAX7219_WriteByte(digit);
        num /= 10;
        if(num == 0)
        {
            break;
        }
    }
}

int main(void)
{
    uint32_t distance;
    uint8_t data;

    GPIO_Config();
    USART_Config();
    MAX7219_Init();

    while(1)
    {
        if(USART_GetFlagStatus(USART1, USART_FLAG_RXNE) == SET)
        {
            data = USART_ReceiveData(USART1);
            if(data == 0xFF)
            {
                GPIO_SetBits(GPIOA, TRIG_Pin);
                delay_us(10);
                GPIO_ResetBits(GPIOA, TRIG_Pin);
                while(GPIO_ReadInputDataBit(GPIOA, ECHO_Pin) == RESET);
                uint32_t start = SysTick->VAL;
                while(GPIO_ReadInputDataBit(GPIOA, ECHO_Pin) == SET);
                uint32_t end = SysTick->VAL;
                distance = (start - end) / 58;
                MAX7219_Display(distance);
            }
        }
    }
}

注意：以上代码仅供参考，您需要根据您的实际硬件情况进行适当的修改和优化。