求大神指点，该如何讲解电路原理，程序在下面
本系统的主要功能如下：
（1）输出电压：范围 0～＋9.9V，步进 0.1V，纹波不大于 10mV；
（2）输出电流：500mA；
（3）输出电压值由数码管（或 LCD）显示；
（4）由“＋”、“－”两键分别控制输出电压步进增减；
（5）直流电源输出±15V，＋5V。
（6）输出电压可预置在 0～9.9V 之间的任意一个值；
（7）用自动扫描代替人工按键，实现输出电压变化（步进 0.1V 不变）；
#include<reg51.h>
#include<math.h>
#define uchar unsigned char
#define uint unsigned int
sbit rs=P2^4;
sbit rw=P2^5;
sbit ea=P2^6;
uchar num,i,key,j=0;
float a2;
uchar keyscan(void);
uchar code table[6]="Please";
uchar code table1[16]=" enter letter...";
uchar code table2[16]="0123456789abcde.";
float table3[6];
uchar code table4[8]="volt(v):";
uchar code table5[6]="error!";
uchar table6[6];
void delay(uint z)
{
uint x,y;
for(x=z;x>0;x--)
for(y=110;y>0;y--);
}
void write_com(uchar com)
{
rs=0;
rw=0;
P0=com;
delay(5);
ea=1;
delay(5);
ea=0;
}
void write_date(uchar date)
{
rs=1;
rw=0;
P0=date;
delay(5);
ea=1;
delay(5);
ea=0;
}
void disvol()
{
write_com(0x80+0x40);
for(num=0;num<8;num++)
{
write_date(table4[num]);
delay(10);
}
}
void init()
{
delay(5);
write_com(0x38);
write_com(0x0c);
write_com(0x06);
write_com(0x01);
write_com(0x80);
for(num=0;num<6;num++)
{
write_date(table[num]);
delay(20);
}
write_com(0x80+0x40);
for(num=0;num<0x10;num++)
{
write_date(table1[num]);
delay(20);
}
}
void diserr()
{
write_com(0x80+0x40);
for(num=0;num<6;num++)
{
write_date(table5[num]);
delay(20);
}
delay(2000);
}
void he_zhi()
{
uint a1,a3,c11,c12;
float b1,b2,b3,b4,c1,c2,h;
if(table3[0]!='.')
{
if(!table3[1])
{
if(j==1)
{
table3[1]='.';
}
}
if(!table3[2])
{
if(j==2)
{
table3[2]='.';
}
}
if(table3[1]=='.')
{
b1=table3[0];
b2=table3[2]/10;
b3=table3[3]/100;
h=b1+b2+b3;
a2=h*256/10;
a3=a2;
a1=a3+1;
c1=a2-a3;
c2=a1-a2;
c11=1000*c1;
c12=1000*c2;
if(c11>c12)
{
P1=a1;
}
else
{
P1=a3;
}
if(j==1)
{
write_com(0x80+0x49);
}
if(j==3)
{
write_com(0x80+0x4b);
}
if(j==4)
{
write_com(0x80+0x4c);
}
}
else if(table3[2]=='.')
{
b1=table3[0]*10;
b2=table3[1];
b3=table3[3]/10;
b4=table3[4]/100;
h=b1+b2+b3+b4;
if(h<=10)
{
a2=h*256/10;
a3=a2;
a1=a3+1;
c1=a2-a3;
c2=a1-a2;
c11=1000*c1;
c12=1000*c2;
if(c11>c12)
{
P1=a1;
}
else
{
if(a3==256)
{
P1=255;
}
else
{
P1=a3;
}
}
if(j==2)
{
write_com(0x80+0x4a);
}
}
else
{
write_com(0x01);
diserr();
}
}
else
{
write_com(0x01);
diserr();
}
}
if(table3[0]=='.')
{
write_com(0x01);
diserr();
}
}
void qingchu(uchar p)
{
uchar z;
for(z=0;z<=5;z++)
{
table3[z]=p;
}
}
void main()
{
init();
delay(4500);
write_com(0x01);
write_com(0x80+0x40);
write_com(0x0f);
disvol();
i=0x80+0x48;
while(1)
{
key=keyscan();
delay(100);
switch(key)
{
case 0xee:write_com(i);
write_date(table2[0]);table3[j]=0;j++; // table2[16]="0123456789abcde."
i++;
break;//0
case 0xde:write_com(i);
write_date(table2[1]);table3[j]=1;j++;
i++;
break;//1
case 0xbe:write_com(i);
write_date(table2[2]);table3[j]=2;j++;
i++;break;//2
case 0x7e:write_com(i);
write_date(table2[3]);table3[j]=3;j++;
i++;break;//3
case 0xed:write_com(i);
write_date(table2[4]);table3[j]=4;j++;
i++;break;//4
case 0xdd:write_com(i);
write_date(table2[5]);table3[j]=5;j++;
i++;break;//5
case 0xbd:write_com(i);
write_date(table2[6]);table3[j]=6;j++;
i++;break;//6
case 0x7d:write_com(i);
write_date(table2[7]);table3[j]=7;j++;
i++;break;//7
case 0xeb:write_com(i);
write_date(table2[8]);table3[j]=8;j++;
i++;break;//8
case 0xdb:write_com(i);
write_date(table2[9]);table3[j]=9;j++;
i++;break;//9
case 0xe7:write_com(i);
write_date(table2[15]);table3[j]='.';j++;
i++;break;
case 0xbb:write_com(i);
table3[j]=table3[j]+0.1 ;
break;
case 0xd7:he_zhi();
i=0x80+0x48;
j=0;
break;
case 0xb7:write_com(0x01);
qingchu(0);
j=0;
disvol();
write_com(0x80+0x48);
i=0x80+0x48;
break;
}
}
}
uchar keyscan(void)
{
uchar cord_h,cord_l;
P3=0x0f;
cord_h=P3&0x0f;
if(cord_h!=0x0f)
{
delay(100);
if(cord_h!=0x0f)
{
cord_h=P3&0x0f;
P3=cord_h|0xf0;
cord_l=P3&0xf0;
return(cord_h+cord_l);
}
}return(0xff);
}
