#include <reg51.h>
#define mode 0x82;

xdata unsigned char Control _at_ 0x8003;
xdata unsigned char Speaker _at_ 0x8000;

xdata unsigned char OUTBIT _at_ 0x9002;
xdata unsigned char OUTSEG _at_ 0x9004;
xdata unsigned char IN     _at_ 0x9001;

code unsigned char KeyTable[] = {
  0x16, 0x15, 0x14, 0xff,
  0x13, 0x12, 0x11, 0x10,
  0x0d, 0x0c, 0x0b, 0x0a,
  0x0e, 0x03, 0x06, 0x09,
  0x0f, 0x02, 0x05, 0x08,
  0x00, 0x01, 0x04, 0x07
};

unsigned char TestKey()
{
   OUTBIT = 0;
   return (~IN & 0x0f);
}

unsigned char GetKey()
{
  unsigned char Pos;
  unsigned char i;
  unsigned char k;

  i = 6;
  Pos = 0x20;
  do {
    OUTBIT = ~ Pos;
    Pos >>= 1;
    k = ~IN & 0x0f;
  } while ((--i != 0) && (k == 0));

  if (k != 0) {
    i *= 4;
    if (k & 2)
      i += 1;
    else if (k & 4)
      i += 2;
    else if (k & 8)
      i += 3;

    OUTBIT = 0;

    return(KeyTable[i]);
  } else return(0xff);
}

/* ================================================================================ */

code unsigned int ToneTable[7] = {
  64578, 64686, 64778, 64821, 64898, 64968, 65029
};

unsigned char PulseCNT;
unsigned char Pulse;
unsigned ToneHigh, ToneLow;

void Timer() interrupt 1
{
  TR0 = 0;
  TH0 = ToneHigh;
  TL0 = ToneLow;
  TR0 = 1;
  Speaker = Pulse;
  Pulse ++;
  PulseCNT--;
}

void main()
{
  unsigned char Key;

  Control = mode;
  OUTSEG = 0;
  Pulse = 0;
  
  TMOD = 0x01;   // 方式 1 , 記時器
  IE   = 0x82;   // EA=1, IT0 = 1
  while (1) {
    while (! TestKey) ;  // 等按鍵
    Key = GetKey();
    if ( (Key >= 1) && (Key <= 7) ) {
      ToneHigh = ToneTable[Key-1] >> 8;
      ToneLow  = ToneTable[Key-1] & 0xff;
      TH0 = ToneHigh;
      TL0 = ToneLow;
      TR0 = 1;

      PulseCNT = 100;
      while (PulseCNT != 0) ;      // 發 100 個脈沖
      Speaker = 0;
      TR0 = 0;
    }
  }
}