org 0000
    ljmp start
org 1000

TAB: DB 0EEH,0DEH,0BEH,7EH,0EDH,0DDH

start:
    mov DPTR,#start
    ;将dptr low,dptr high压栈，保存start地址，以便ret指令返回
    push dpl
    push dph

    mov A,#0EEH
    mov 20H,A

    ;置键码表TAB表首地址
    ;A为表起始地址偏移量
    mov DPTR,#TAB
    mov A,#0 

next:
    ;保存A寄存器中的值
    push acc
    movc A,@A+DPTR  ;A为TAB编码
    ;讲20H的值与A比较，如果不相等跳转
    CJNE A,20H,notequal
    ;如果相等
    pop acc
    RL A            ;得分支表内部偏移（x2,8位变16位)
    mov DPTR,#APJ   ;置分支表首地址
    JMP @A+DPTR     ;执行表跳转

notequal:
    pop acc
    inc A
    ;如果A的值为6退出循环
    CJNE A,#6,next
    SJMP $

APJ:
    AJMP PR0
    AJMP PR1
    AJMP PR2
    AJMP PR3
    AJMP PR4

;RET 返回指令，就会用刚刚压入两字节数据，当做返回地址。
PR0:
    RET
PR1:
    RET
PR2:
    RET 
PR3:
    RET 
PR4:
    RET 

end
    

#include<reg51.h>

void PR2();
void PR0();
void PR1();

void main() {
    PR2();
}

//P75-7
void PR0() {
    char i;
    //声明存储单元指针
    char *Ppos  = 0x40;
    char *Pneg  = 0x50;
    char *Pdata = 0x30;

    //声明计数变量
    char R4 = 0;    //pos
    char R5 = 0;    //neg
    char R6 = 0;    //zero

    //定义数据
    char datas[16] = {2,4,6,8,10,0,-1,-3,-5,-7,-9};


    //数据存入0x30
    //正数存入0x40,负数存入0x50

    for(i=0; i<16; i++) {
        *(Pdata++) = datas[i];

        if(datas[i]>0) {
            *(Ppos++) = datas[i];
            R4++;
        }

        if(datas[i]<0) {
            *(Pneg++) = datas[i];
            R5++;
        }

        if(datas[i]==0) {
            R6++;
        }

    }
}

//P75-9

void PR1() {
#define DATA 0X10
    char ADC=0;
    char i=0;
    char data *d = DATA;
    //定义4字节数
    *d     = 0xAA;
    *(d+1) = 0xAA;
    *(d+2) = 0xAA;
    *(d+3) = 0xAA;

    //进位标志

    //逐字节取反
    for(i=0; i<4; i++) {
        *(d+i) = ~*(d+i);
    }
    //加一
    if(*d==0xFF) {
        *d=0;
        ADC=1;
    } else {
        //加一
        (*d)++;
        //d->d+1
        d++;
    }

    for(i=1; i<4; i++) {
        //如果此字节为FF且有进位
        if(*d==0xFF&&ADC==1) {
            ADC=1;
            *d=0;
        }
        //此字节不为FF但有进位
        else if(ADC==1) {
            (*d)++;
            ADC=0;
        }
        d++;
    }

}


void PR2() {
#define BUF1 0x60
#define BUF2 0x10
#define BUF 0x00
    //定义数据
    unsigned char sets[16] = {0x05,0x0F,0x02,0x03,0x04,0x05,0x06,0x07,0x08,0x09,0x0A,0x0B,0x0C,0x0D,0x0E,0x0F};
    unsigned char sum=0;
    unsigned char avg=0;
    unsigned char rem=0;
    char i;
    unsigned char xdata *dx     = BUF1;
    unsigned char data *davg    = BUF2;
    unsigned char data *drem    = BUF;

    //存储外部数据
    for(i=0; i<16; i++) {
        *dx = sets[i];
        dx++;
    }
    //恢复dx起始地址
    dx = BUF1;
    //求累加值
    for(i=0; i<16; i++) {
        sum += *dx;
        dx++;
    }

    avg = sum/16;
    rem = sum%16;

    *davg = avg;
    *drem = rem;



}