跪求单片机高手啊，关于中断和PID控制的问题。

#include <include.h>
uint cycle_time=0;
bit dis_flag=1;uchar counter=0;
double kp=0.06615,Ti=0.49,Td=0.14,T=0.014,UU;
double b1, b2, b3;
int E1; //误差的数字量
float e[3]={0}; //误差的模拟量
float u=0,u1;//u为PID输出的控制量，u1为控制量增量
int UX; //控制量的数字量
int wendusheding=20;
float wendu;
float u_temp;
uchar dis_temp1;
bit cold_flag,hot_flag;
uchar TH0_temp;
bit zheng_flag;
void display();
void key_check();
void timer0_init();
void pid_c();
void adc0809();
void baojing();
void dely()
{int i;
for(i=0;i<=20;i++);}
void key_check()
{if(add==0)
{delay_1ms(20);
if(add==0)
{if(wendusheding<80)wendusheding++;while(!add);}}
if(dec==0)
{delay_1ms(20);
if(dec==0)
{if(wendusheding>0)wendusheding--;while(!dec);}}}
void pid_c()
{ e[2]=(wendu-wendusheding)/256*5;
u1=b1*e[2]+b2*e[1]+b3*e[0];
u=u+u1;
if(u>=1) u=1;
if(u<=-1) u=-1;
e[0]=e[1];
e[1]=e[2];
if(u>=0)
{ cold_flag=1;
hot_flag=0;
TH0_temp=(uchar)(u*255); }
else { cold_flag=0;
hot_flag=1;
u_temp=0-u;
TH0_temp=(uchar)(u_temp*255); }
}
void adc0809(){
start=1; //启动转换信号 dely(); start=0; while(eoc==1); //判断是否转换完成 oe=1; //OE输入高电平时，输出三态门打开，转换结果的数字量输出到数据总线上 E1=P0;
wendu=E1*3.7-270;
baojing();
lcd1602_pos(0x40); lcd1602_wdat('S'); lcd1602_wdat('J'); lcd1602_wdat('W'); lcd1602_wdat('D'); lcd1602_wdat(':'); lcd1602_wdat(' '); dis_temp1=wendu/100; if(dis_temp1!=0) lcd1602_wdat(0x30+wendu/100); else lcd1602_wdat(' '); dis_temp1=(uchar)wendu; dis_temp1=(uchar)((dis_temp1/10)%10); lcd1602_wdat(0x30+dis_temp1); dis_temp1=(uchar)wendu; lcd1602_wdat(0x30+dis_temp1%10); lcd1602_wdat('C');
}
void timer0_init() //定时50ms中断设置
{
TMOD=0x11; //定时器的工作方式
TH0=0x3c;
TL0=0xb0; //给定时器T0设置初值，高八位，低八位，50ms
EA=1; //中断总允许
ET0=1; //T0中断允许
TR0=1; //T0工作开始
}
timer0()interrupt 1 using 1
{
TL0=0;
if(zheng_flag==0)
{
TH0=TH0_temp;
zheng_flag=1;
if(hot_flag==1)
{hot=0;
cold=1;}
if(cold_flag==1)
{hot=1;
cold=0;}
}
else
{TH0=255-TH0_temp;
zheng_flag=0;
hot=1;
cold=1;
}
}
void display(){ uchar temp2; lcd1602_pos(0x00); delay_1ms(1); lcd1602_wdat('Y'); delay_1ms(1); lcd1602_wdat('S'); delay_1ms(1); lcd1602_wdat('W'); delay_1ms(1); lcd1602_wdat('D'); delay_1ms(1); lcd1602_wdat(':'); delay_1ms(1); lcd1602_wdat(' '); delay_1ms(1); temp2=wendusheding/100; if(temp2!=0) lcd1602_wdat(0x30+temp2); else lcd1602_wdat(' '); delay_1ms(1); temp2=wendusheding/10%10; lcd1602_wdat(0x30+temp2); temp2=wendusheding%10; lcd1602_wdat(0x30+temp2); lcd1602_wdat('C'); delay_1ms(1);}
void baojing(){ if(wendu>(wendusheding+2)||wendu<(wendusheding-2)) SPK=0; else SPK=1;}
void main()
{
delay_1ms(50);
lcd1602_init();
timer0_init();
delay_1ms(1);
b1=kp*(1+T/Ti+Td/T);
b2=-kp*(1+2*Td/T);
b3=kp*Td/T;
while(1)
{
adc0809();
key_check();
display();
pid_c();
}
}
这是一个恒温控制的系统，看不懂中断和PID这两块。跪求大侠讲解下。谢了。