简易波形发生器

#include <REG51.H>
sbit key0 = P3^0;
sbit key1 = P3^1;
sbit key2 = P3^2;
sbit key3 = P3^3;
sbit key4 = P3^4;
code unsigned char sin_tab[] =
{
0x7F,0x82,0x85,0x88,0x8B,0x8F,0x92,0x95,0x98,0x9B,0x9E,0xA1,0xA4,0xA7,0xAA,0xAD
,0xB0,0xB3,0xB6,0xB8,0xBB,0xBE,0xC1,0xC3,0xC6,0xC8,0xCB,0xCD,0xD0,0xD2,0xD5,0xD7
,0xD9,0xDB,0xDD,0xE0,0xE2,0xE4,0xE5,0xE7,0xE9,0xEB,0xEC,0xEE,0xEF,0xF1,0xF2,0xF4
,0xF5,0xF6,0xF7,0xF8,0xF9,0xFA,0xFB,0xFB,0xFC,0xFD,0xFD,0xFE,0xFE,0xFE,0xFE,0xFE
,0xFE,0xFE,0xFE,0xFE,0xFE,0xFE,0xFD,0xFD,0xFC,0xFB,0xFB,0xFA,0xF9,0xF8,0xF7,0xF6
,0xF5,0xF4,0xF2,0xF1,0xEF,0xEE,0xEC,0xEB,0xE9,0xE7,0xE5,0xE4,0xE2,0xE0,0xDD,0xDB
,0xD9,0xD7,0xD5,0xD2,0xD0,0xCD,0xCB,0xC8,0xC6,0xC3,0xC1,0xBE,0xBB,0xB8,0xB6,0xB3
,0xB0,0xAD,0xAA,0xA7,0xA4,0xA1,0x9E,0x9B,0x98,0x95,0x92,0x8F,0x8B,0x88,0x85,0x82
,0x7F,0x7C,0x79,0x76,0x73,0x6F,0x6C,0x69,0x66,0x63,0x60,0x5D,0x5A,0x57,0x54,0x51
,0x4E,0x4B,0x48,0x46,0x43,0x40,0x3D,0x3B,0x38,0x36,0x33,0x31,0x2E,0x2C,0x29,0x27
,0x25,0x23,0x21,0x1E,0x1C,0x1A,0x19,0x17,0x15,0x13,0x12,0x10,0x0F,0x0D,0x0C,0x0A
,0x09,0x08,0x07,0x06,0x05,0x04,0x03,0x03,0x02,0x01,0x01,0x00,0x00,0x00,0x00,0x00
,0x00,0x00,0x00,0x00,0x00,0x00,0x01,0x01,0x02,0x03,0x03,0x04,0x05,0x06,0x07,0x08
,0x09,0x0A,0x0C,0x0D,0x0F,0x10,0x12,0x13,0x15,0x17,0x19,0x1A,0x1C,0x1E,0x21,0x23
,0x25,0x27,0x29,0x2C,0x2E,0x31,0x33,0x36,0x38,0x3B,0x3D,0x40,0x43,0x46,0x48,0x4B
,0x4E,0x51,0x54,0x57,0x5A,0x5D,0x60,0x63,0x66,0x69,0x6C,0x6F,0x73,0x76,0x79,0x7C
};
//void delay_ms(unsigned int ms)
//{
// unsigned char i;
// while(ms--)
//    for(i = 0;i<120;i++);
//}
#define duan P0
#define wei P2
unsigned  char code duan_ma[] = {0xc0,0xf9,0xa4,0xb0,0x99,0x92,
0x82,0xf8,0x80,0x90,};//黄板 共阳
unsigned char code wei_ma[]= {0xfe,0xfd,0xfb,0xf7,0xef,0xdf,0xbf,0x7f};
void led_show_delay_us(unsigned int us)//微秒级的延时
{
while(us--);
}
void led_show_number(unsigned char len,unsigned long int num)
{
  unsigned char n;
unsigned char temp[8];
    temp[7] =  num%100000000/10000000;
temp[6]  = num%10000000/1000000;
temp[5]  = num%1000000/100000;
temp[4]  = num%100000/10000;
temp[3]  = num%10000/1000;
temp[2]  = num%1000/100;
temp[1]  = num%100/10;
temp[0]  = num%10;
if(len>8) len =8;
for(n = 0;n<len;n++)
{
   wei = wei_ma[n];
  duan = duan_ma[temp[n]];
  led_show_delay_us(100);
}
}
void main()
{
unsigned char n,us,vol = 1,sta = 0;
while(1)
  {
       if(key0 == 0)
    {
     while(！key0);
  vol--;
  if(vol<1)vol = 1;
    }
     if(key1 == 0)
    {
     while(！key1);
  vol++;
  if(vol>3)vol = 3;
    }
    if(key2 == 0)
    {
     while(！key2);
  us--;
    }
     if(key3 == 0)
    {
     while(！key3);
  us++;
    }
     if(key4 == 0)
    {
     while(！key4);
  sta++;
  if(sta>4) sta =0;
    }
    switch(sta)
    {
       case 0:
     n++;
     P1 = sin_tab[n]/vol;   //正玄波
     led_show_delay_us(us);
    break;
    case 1:
     n++;
     P1 = n/vol;
     led_show_delay_us(us); //锯齿波
    break;
    case 2:
    for(n = 0;n<255;n++)
    {
     P1 = n/vol;
     led_show_delay_us(us);
    }        //三角波
    for(n = 255;n>0;n--)
    {
     P1 = n/vol;
     led_show_delay_us(us);
    }
    break;
    case 3:
      P1 = n/vol;
     led_show_delay_us(us);       //方波
     P1 = ~n/vol;
     led_show_delay_us(us);  break;
    }
     }
}为什么到方波时就不得了啊?会出现失真的现象啊?