通过单片机的P1.5控制无源蜂鸣器演奏天空之城；

要控制无源蜂鸣器演奏天空之城，需要使用单片机的PWM输出功能。以下是一个基本的代码示例，假设使用的是51单片机，无源蜂鸣器连接在P1.5口：

#include <reg51.h>

#define BUZZER P1.5

// 定义每个音符的频率，单位为Hz
#define NOTE_C4  262
#define NOTE_D4  294
#define NOTE_E4  330
#define NOTE_F4  349
#define NOTE_G4  392
#define NOTE_A4  440
#define NOTE_B4  494

// 定义每个音符的持续时间，单位为毫秒
#define DURATION_QUARTER_NOTE  500
#define DURATION_HALF_NOTE     1000
#define DURATION_WHOLE_NOTE    2000

// 定义天空之城的旋律，用数字代表每个音符
int melody[] = {
  NOTE_E4, NOTE_G4, NOTE_A4, NOTE_B4,
  NOTE_A4, NOTE_G4, NOTE_E4, NOTE_E4,
  NOTE_G4, NOTE_A4, NOTE_B4, NOTE_A4,
  NOTE_G4, NOTE_E4, NOTE_E4, NOTE_G4,
  NOTE_A4, NOTE_B4, NOTE_A4, NOTE_G4,
  NOTE_E4, NOTE_E4, NOTE_D4, NOTE_D4,
  NOTE_E4, NOTE_G4, NOTE_A4, NOTE_B4,
  NOTE_A4, NOTE_G4, NOTE_E4, NOTE_E4
};

// 定义天空之城的每个音符的持续时间
int noteDurations[] = {
  DURATION_QUARTER_NOTE, DURATION_QUARTER_NOTE, DURATION_QUARTER_NOTE, DURATION_QUARTER_NOTE,
  DURATION_QUARTER_NOTE, DURATION_QUARTER_NOTE, DURATION_HALF_NOTE, DURATION_QUARTER_NOTE,
  DURATION_QUARTER_NOTE, DURATION_QUARTER_NOTE, DURATION_QUARTER_NOTE, DURATION_QUARTER_NOTE,
  DURATION_QUARTER_NOTE, DURATION_QUARTER_NOTE, DURATION_HALF_NOTE, DURATION_QUARTER_NOTE,
  DURATION_QUARTER_NOTE, DURATION_QUARTER_NOTE, DURATION_QUARTER_NOTE, DURATION_QUARTER_NOTE,
  DURATION_QUARTER_NOTE, DURATION_QUARTER_NOTE, DURATION_HALF_NOTE, DURATION_HALF_NOTE,
  DURATION_QUARTER_NOTE, DURATION_QUARTER_NOTE, DURATION_QUARTER_NOTE, DURATION_QUARTER_NOTE,
  DURATION_QUARTER_NOTE, DURATION_QUARTER_NOTE, DURATION_HALF_NOTE, DURATION_QUARTER_NOTE
};

void delay(unsigned int ms) {
  unsigned int i, j;
  for (i = 0; i < ms; i++) {
    for (j = 0; j < 114; j++);
  }
}

void playNote(int noteFrequency, int duration) {
  int i;
  int halfPeriod = 1000000 / noteFrequency / 2; // 计算半个周期的时间，单位为微秒
  int cycles = duration * 1000 / halfPeriod; // 计算需要输出的周期数
  for (i = 0; i < cycles; i++) {
    BUZZER = 1; // 输出高电平
    delay(halfPeriod / 1000); // 延时半个周期时间
    BUZZER = 0; // 输出低电平
    delay(halfPeriod / 1000); // 延时半个周期时间
  }
}

void main() {
  int i;
  TMOD = 0x01; // 定时器0作为定时器
  TH0 = 0x3c;
  TL0 = 0xb0;
  TR0 = 1; // 启动定时器0
  while (1) {
    for (i = 0; i < sizeof(melody) / sizeof(melody[0]); i++) {
      int noteDuration = noteDurations[i];
      int noteFrequency = melody[i];
      playNote(noteFrequency, noteDuration);
      delay(noteDuration * 1.3); // 延时一点以保证音符之间有间隔
    }
  }
}

这段代码使用了定时器0来定时，通过占空比来产生PWM波形控制蜂鸣器发声。需要注意的是，无源蜂鸣器没有内部驱动，需要使用PWM来控制其振动频率。此外，为了保证音符之间有间隔，需要在每个音符结束后延时一小段时间。