波形发生器：（1）基础功能：采用DAC实现输出至少三种波形（三角波、矩形波、正弦波）；（2）发挥部分：按键控制输出波的频率和幅度。

好的，以下是一个基于DAC的51单片机波形发生器程序，可供参考：

#include <reg51.h>

#define FREQ_MIN 100   // 最小频率
#define FREQ_MAX 10000 // 最大频率
#define AMP_MIN  0     // 最小幅度
#define AMP_MAX  255   // 最大幅度

unsigned char sine_table[] = {
  128, 131, 134, 137, 140, 143, 146, 149,
  152, 155, 158, 161, 165, 168, 171, 174,
  177, 180, 183, 186, 189, 192, 195, 198,
  201, 204, 207, 210, 213, 216, 218, 221,
  224, 227, 230, 233, 236, 239, 241, 244,
  247, 250, 252, 255, 257, 260, 263, 265,
  268, 270, 273, 275, 277, 280, 282, 284,
  287, 289, 291, 293, 295, 297, 299, 301,
  303, 304, 306, 308, 309, 311, 312, 314,
  315, 316, 318, 319, 320, 321, 322, 323,
  324, 325, 326, 326, 327, 327, 327, 327,
  327, 327, 327, 326, 326, 325, 324, 323,
  322, 321, 320, 319, 318, 316, 315, 314,
  312, 311, 309, 308, 306, 304, 303, 301,
  299, 297, 295, 293, 291, 289, 287, 284,
  282, 280, 277, 275, 273, 270, 268, 265,
  263, 260, 257, 255, 252, 250, 247, 244,
  241, 239, 236, 233, 230, 227, 224, 221,
  218, 216, 213, 210, 207, 204, 201, 198,
  195, 192, 189, 186, 183, 180, 177, 174,
  171, 168, 165, 161, 158, 155, 152, 149,
  146, 143, 140, 137, 134, 131, 128, 124,
  121, 118, 115, 112, 109, 106, 103, 100,
  97,  94,  91,  88,  85,  81,  78,  75,
  72,  69,  66,  63,  60,  57,  54,  51,
  48,  45,  42,  39,  37,  34,  31,  28,
  25,  22,  19,  16,  13,  10,  8,   5,
  2,   0,   0,   0,   0,   0,   0,   0,
  0,   0,   0,   0,   0,   0,   0,   0,
  0,   0,   0,   0,   0,   0,   0,   0,
  2,   5,   8,   10,  13,  16,  19,  22,
  25,  28,  31,  34,  37,  39,  42,  45,
  48,  51,  54,  57,  60,  63,  66,  69,
  72,  75,  78,  81,  85,  88,  91,  94,
  97,  100, 103, 106, 109, 112, 115, 118,
  121, 124
};

unsigned char saw_table[] = {
  0,   6,   12,  18,  24,  30,  36,  42,
  48,  54,  60,  66,  72,  78,  84,  90,
  96,  102, 108, 114, 120, 126, 132, 138,
  144, 150, 156, 162, 168, 174, 180, 186,
  192, 198, 204, 210, 216, 222, 228, 234,
  240, 246, 252, 0,   6,   12,  18,  24,
  30,  36,  42,  48,  54,  60,  66,  72,
  78,  84,  90,  96,  102, 108, 114, 120,
  126, 132, 138, 144, 150, 156, 162, 168,
  174, 180, 186, 192, 198, 204, 210, 216,
  222, 228, 234, 240, 246, 252, 0,   6,
  12,  18,  24,  30,  36,  42,  48,  54,
  60,  66,  72,  78,  84,  90,  96,  102,
  108, 114, 120, 126, 132, 138, 144, 150,
  156, 162, 168, 174, 180, 186, 192, 198,
  204, 210, 216, 222, 228, 234, 240, 246,
  252, 0,   6,   12,  18,  24,  30,  36,
  42,  48,  54,  60,  66,  72,  78,  84,
  90,  96,  102, 108, 114, 120, 126, 132,
  138, 144, 150, 156, 162, 168, 174, 180,
  186, 192, 198, 204, 210, 216, 222, 228,
  234, 240, 246, 252
};

unsigned char square_table[] = {
  0, 0, 0, 0, 0, 0, 0, 0,
  255, 255, 255, 255, 255, 255, 255, 255
};

unsigned int freq = 1000;  // 波形频率
unsigned char amp = 127;   // 波形幅度
unsigned char wave_type = 0;  // 波形类型：0-正弦波，1-三角波，2-矩形波

void delay() {
  unsigned int i = 10000;
  while (i--);
}

void dac_out(unsigned char val) {
  P0 = val;
}

void main() {
  unsigned char i = 0;   // 波形数据计数器
  unsigned char j = 0;   // 按键扫描计数器
  unsigned char k = 0;   // 波形类型计数器
  unsigned char key = 0; // 按键状态

  TMOD = 0x01;           // 定时器0工作在模式1
  TH0 = 0 - (freq / 1000000.0 * 12 / 2);   // 定时器0初始值
  TL0 = TH0;             // 定时器0初始值
  TR0 = 1;               // 启动定时器0

  while (1) {
    if (TF0) {           // 定时器0溢出中断
      TF0 = 0;           // 清除