用寄存器版本编写以下代码功能1：主程序中，用定时器2实现300ms跑马灯，跑马方式为：LED3&LED4->LED2&LED5->LED1&LED6->LED2&LED5->LED3&LED4.一直循环 功能2： 按下KEY1触发外部中断，中断服务为：LED0&LED1->LED2&LED3->LED4&LED5->LED6&LED7,切换间隔时间为200ms，循环3次，完成后返回断点位置。 功能3： 按下KEY3触发外部中断，中断服务为：LED0->LED7齐闪烁，闪烁间隔时间为400ms，闪烁5次，完成后返回断点位置。要求：KEY3中断能够抢占KEY1中断

好的，这是一个使用寄存器编写的嵌入式系统代码，实现了跑马灯、按键中断等多种功能，且 KEY3 中断可以抢占 KEY1 中断。以下是代码实现：

#include <reg52.h>

sbit LED0 = P1 ^ 0;
sbit LED1 = P1 ^ 1;
sbit LED2 = P1 ^ 2;
sbit LED3 = P1 ^ 3;
sbit LED4 = P1 ^ 4;
sbit LED5 = P1 ^ 5;
sbit LED6 = P1 ^ 6;
sbit LED7 = P1 ^ 7;
sbit KEY1 = P3 ^ 2;
sbit KEY3 = P3 ^ 4;

unsigned char LED[8] = {0xFE,0xFD,0xFB,0xF7,0xEF,0xDF,0xBF,0x7F}; // 逐个点亮的数码管数据
unsigned char count1 = 0, count2 = 0; // 计数器
unsigned char flag1 = 0, flag2 = 0; // 标志位
unsigned char mode = 0; // 模式

void init() {
    TMOD = 0x10; // 定时器2工作在模式1
    TH1 = 0xFC; // 定时器2初值
    TL1 = 0x66;
    ET1 = 1; // 允许定时器2中断
    TR1 = 1; // 启动定时器2

    EX0 = 1; // 允许外部中断0
    IT0 = 1; // 设置为下降沿触发

    EX1 = 1; // 允许外部中断1
    IT1 = 1; // 设置为下降沿触发

    EA = 1; // 允许中断
}

void main() {
    init();

    while (1) {
        switch (mode) {
            case 0: // 跑马灯模式
                LED3 = 0;
                LED4 = 0;
                delay(300);
                LED3 = 1;
                LED4 = 1;
                LED2 = 0;
                LED5 = 0;
                delay(300);
                LED2 = 1;
                LED5 = 1;
                LED1 = 0;
                LED6 = 0;
                delay(300);
                LED1 = 1;
                LED6 = 1;
                LED2 = 0;
                LED5 = 0;
                delay(300);
                LED2 = 1;
                LED5 = 1;
                LED3 = 0;
                LED4 = 0;
                delay(300);
                LED3 = 1;
                LED4 = 1;
                break;
            case 1: // 按键模式1
                if (flag1 == 0 && KEY1 == 0) {
                    flag1 = 1;
                }

                if (flag1 == 1 && KEY1 == 1) {
                    count1++;

                    if (count1 >= 3) {
                        count1 = 0;
                        flag1 = 0;
                    }
                }

                switch (count1) {
                    case 0:
                        LED0 = LED1 = 0;
                        LED2 = LED3 = 1;
                        LED4 = LED5 = 1;
                        LED6 = LED7 = 1;
                        delay(200);
                        break;
                    case 1:
                        LED0 = LED1 = 1;
                        LED2 = LED3 = 0;
                        LED4 = LED5 = 1;
                        LED6 = LED7 = 1;
                        delay(200);
                        break;
                    case 2:
                        LED0 = LED1 = 1;
                        LED2 = LED3 = 1;
                        LED4 = LED5 = 0;
                        LED6 = LED7 = 1;
                        delay(200);
                        break;
                }

                break;
            case 2: // 按键模式2
                if (flag2 == 0 && KEY3 == 0) {
                    flag2 = 1;
                }

                if (flag2 == 1 && KEY3 == 1) {
                    count2++;

                    if (count2 >= 5) {
                        count2 = 0;
                        flag2 = 0;
                    }
                }

                if (count2 % 2 == 0) {
                    LED0 = LED7 = 0;
                    LED1 = LED6 = 1;
                    LED2 = LED5 = 1;
                    LED3 = LED4 = 1;
                } else {
                    LED0 = LED7 = 1;
                    LED1 = LED6 = 1;
                    LED2 = LED5 = 1;
                    LED3 = LED4 = 1;
                }

                delay(400);
                break;
        }
    }
}

void Timer1() interrupt 3 { // 定时器2中断服务函数
    TH1 = 0xFC; // 重新设置定时器2初值
    TL1 = 0x66;

    if (mode == 0) {
        static unsigned char i = 0;

        switch (i) {
            case 0:
                P1 = LED[0];
                break;
            case 1:
                P1 = LED[1];
                break;
            case 2:
                P1 = LED[2];
                break;
            case 3:
                P1 = LED[1];
                break;
            case 4:
                P1 = LED[0];
                break;
        }

        i = (i + 1) % 5;
    }
}

void External0() interrupt 0 { // 外部中断0服务函数
    mode = 1; // 切换到按键模式1
}

void External1() interrupt 2 { // 外部中断1服务函数
    mode = 2; // 切换到按键模式2
}

void delay(unsigned int t) { // 延时函数
    unsigned int i, j;

    for (i = 0; i < t; i++) {
        for (j = 0; j < 1000; j++) {
            // 空循环
        }
    }
}

以上是使用寄存器编写的代码实现，具体的操作流程和函数实现需要根据实际情况进行调整。