如何通过代码实现51单片机交通灯; (考察知识: LED， 串口，定时器中断的综合应用) 单片机上电后，红灯亮，高10s,前7秒常高，后3秒闪烁，串口给上位机发送“禁止通行”红灯灭后，绿灯亮8s，前5秒常高，后3秒闪烁，串口给上位机发送“允许通行” 绿灯灭后，黄灯高6s，前3秒常亮，后3秒闪烁，串口给上位机发送“等待通行

以下是一个可能的实现代码，仅供参考：

#include <reg51.h>

#define LED_RED P0_0
#define LED_GREEN P0_1
#define LED_YELLOW P0_2

#define UART_BAUDRATE 9600
#define UART_TIMER_PRESCALER 12

// 定义定时器计数值
#define TIMER_1S 1000
#define TIMER_3S 3000
#define TIMER_5S 5000
#define TIMER_7S 7000
#define TIMER_8S 8000
#define TIMER_10S 10000

// 定义串口发送的消息
#define MSG_RED "禁止通行"
#define MSG_GREEN "允许通行"
#define MSG_YELLOW "等待通行"

// 定义当前的灯的状态
typedef enum {
    STATE_RED,
    STATE_GREEN,
    STATE_YELLOW
} State;

// 定义当前的灯的状态、计时器、闪烁计数器等变量
volatile State g_state = STATE_RED;
volatile unsigned int g_timer = TIMER_10S;
volatile unsigned int g_blink_count = 0;
volatile unsigned char g_blink_state = 0;

// 初始化定时器
void timer_init() {
    TMOD |= 0x10;  // 设置定时器1为工作方式1
    TH1 = 0xFC;    // 设置定时器1的初始值，使定时器1开始计时时为1ms
    TL1 = 0x18;
    ET1 = 1;       // 打开定时器1中断
    TR1 = 1;       // 启动定时器1
}

// 定时器1中断，每隔1ms执行一次
void timer1_isr() interrupt 3 {
    g_timer--;
    if (g_timer == 0) {
        switch (g_state) {
            case STATE_RED:
                g_state = STATE_GREEN;
                g_timer = TIMER_8S;
                g_blink_count = 0;
                LED_RED = 0;
                LED_GREEN = 1;
                SBUF = MSG_GREEN;
                break;
            case STATE_GREEN:
                g_state = STATE_YELLOW;
                g_timer = TIMER_6S;
                g_blink_count = 0;
                LED_GREEN = 0;
                LED_YELLOW = 1;
                SBUF = MSG_YELLOW;
                break;
            case STATE_YELLOW:
                g_state = STATE_RED;
                g_timer = TIMER_10S;
                g_blink_count = 0;
                LED_YELLOW = 0;
                LED_RED = 1;
                SBUF = MSG_RED;
                break;
            default:
                break;
        }
    } else {
        switch (g_state) {
            case STATE_RED:
                if (g_timer == TIMER_7S) {
                    LED_RED = 0;
                } else if (g_timer == TIMER_3S) {
                    g_blink_state = 1;
                }
                break;
            case STATE_GREEN:
                if (g_timer == TIMER_5S) {
                    LED_GREEN = 0;
                } else if (g_timer == TIMER_3S) {
                    g_blink_state = 1;
                }
                break;
            case STATE_YELLOW:
                if (g_timer == TIMER_3S) {
                    LED_YELLOW = 0;
                } else if (g_timer == TIMER_6S) {
                    g_blink_state = 1;
                }
                break;
            default:
                break;
        }
        if (g_blink_state && g_blink_count < 6) {
            g_blink_count++;
            if (g_state == STATE_RED) {
                LED_RED = ~LED_RED;
            } else if (g_state == STATE_GREEN) {
                LED_GREEN = ~LED_GREEN;
            } else {
                LED_YELLOW = ~LED_YELLOW;
            }
        } else {
            g_blink_state = 0;
        }
    }
}

// 初始化串口
void uart_init() {
    SCON = 0x50;  // 设置串口为工作方式1，允许接收
    TMOD |= 0x20; // 设置定时器1为工作方式2
    TH1 = 256 - (11059200 / 12 / UART_BAUDRATE); // 设置波特率
    TL1 = TH1;
    ET1 = 0; // 关闭定时器1中断
    TR1 = 1; // 启动定时器1
}

// 串口发送一个字符
void uart_send_char(unsigned char c) {
    SBUF = c;
    while (!TI); // 等待发送完成
    TI = 0;
}

// 串口发送一个字符串
void uart_send_string(const char* s) {
    while (*s) {
        uart_send_char(*s++);
    }
}

void main() {
    LED_RED = 1;
    timer_init();
    uart_init();
    SBUF = MSG_RED;
    while (1);
}

该代码中使用了定时器1来控制交通灯状态的切换和LED闪烁，使用串口发送消息。注意，由于定时器1需要和串口使用同一个计数器，因此串口发送消息时需要关闭定时器1中断。同时，在发送完消息后，需要重新打开定时器1中断。