Arduino DSC PC1500RK Interface

/*
    The code is to interface a DSC PC1500RK alarm keypad.
        It has 15 keys, 11 LEDs, and a Beeper that can be controlled.
        This code cycles through all the LEDs in a top-down fashion.
        The beeper is used to acknowledge that a key has been pressed.
        If the key was pressed successfully, its character is output on the serial line, at 9600 bps.

    I was originally communicating at 115200, but due to the read speed, and also the tendency to
    quickly overfill the read buffer if lots of commands are sent at once, I slowed it down to 9600.
    It is still possible to overfill the buffer, but that is mainly if you sends tons of flag
    altering commands, or if you send a bunch of beep/delay commands all at once.
    The general thing, is Hurry up and wait. :).
        (In other words, maintain a slower pace whenever possible.)

    The fastest that this keypad can be read out, is ~30 times a second.  I tried doing 500
    microsecond delays between clock cycles, and things started becoming unresponsive.

        Wiring is simple.  Red is Vcc, hooked to 5V
        Black is Gnd.
        Yellow is the Clock line. In this configuration, it is on Digital Pin 3.
        Green is Data, and is on Digital Pin 2.

        Beeper      0x0001
        unknown     0x0002
        unknown     0x0004
        Trouble LED 0x0008
        By-Pass LED 0x0010
        Memory LED  0x0020
        Armed LED   0x0040
        Ready LED   0x0080
        unknown     0x0100
        unknown     0x0200
        Zone 6 LED  0x0400
        Zone 5 LED  0x0800
        Zone 4 LED  0x1000
        Zone 3 LED  0x2000
        Zone 2 LED  0x4000
        Zone 1 LED  0x8000

        Matrix output is in the format of RCCCRRRR.
        Matrix Output   Key     Output ^ 0xFF
        11111111    -Nothing    0x00
        10111110    1       0x41
        11011110    2       0x21
        11101110    3       0x11
        10111101    4       0x42
        11011101    5       0x22
        11101101    6       0x12
        10111011    7       0x44
        11011011    8       0x24
        11101011    9       0x14
        10110111    *       0x48
        11010111    0       0x28
        11100111    #       0x18
        00111111    F       0xC0
        01011111    E       0xA0
        01101111    P       0x90
*/

#define CLOCKPIN 3
#define DATAPIN 2

#define NO_FLAGS 0x0000
#define BUZZER 0x0001
#define TROUBLE 0x0008
#define BYPASS 0x0010
#define MEMORY 0x0020
#define ARMED 0x0040
#define READY 0x0080
#define ZONE_1 0x8000
#define ZONE_2 0x4000
#define ZONE_3 0x2000
#define ZONE_4 0x1000
#define ZONE_5 0x0800
#define ZONE_6 0x0400

#define NO_KEY_PRESSED 0


void setup() {
  //Pin 2 is Data, and is bidirectional.
  //Pin 3 is Clock, and is an output.
  pinMode(DATAPIN, OUTPUT);
  pinMode(CLOCKPIN, OUTPUT);
  Serial.begin(9600);    //Any faster, and we run the risk of doing hurry up and wait.
}

int readdata(int control)
{

  int i,j=0,k=control;
  int bitcount=0;

  for(i=0;i<8;i++)
  {
    j<<=1;
    digitalWrite(DATAPIN,HIGH);
    digitalWrite(CLOCKPIN,LOW);
    delayMicroseconds(625);
    //delay(1);
    if(digitalRead(DATAPIN)==LOW)
      j|=1;
    digitalWrite(CLOCKPIN,HIGH);
    delayMicroseconds(625);
    //delay(1);
  }
  for(i=0;i<16;i++)
  {
    if(k&0x8000)
      digitalWrite(DATAPIN,HIGH);
    else
      digitalWrite(DATAPIN,LOW);
    digitalWrite(CLOCKPIN,LOW);
    delayMicroseconds(625);
    //delay(1);
    digitalWrite(CLOCKPIN,HIGH);
    delayMicroseconds(625);
    //delay(1);
    k<<=1;
  }
  if(j==0x41) return '1';
  if(j==0x42) return '4';
  if(j==0x44) return '7';
  if(j==0x48) return '*';
  if(j==0x21) return '2';
  if(j==0x22) return '5';
  if(j==0x24) return '8';
  if(j==0x28) return '0';
  if(j==0x11) return '3';
  if(j==0x12) return '6';
  if(j==0x14) return '9';
  if(j==0x18) return '#';
  if(j==0x90) return 'P';
  if(j==0xA0) return 'E';
  if(j==0xC0) return 'F';
  return 0;
}

void loop() {
  int i;


  static int last_key_pressed=0,key_just_pressed;
  static unsigned int flags=0x80;
  static unsigned int buzzer_counter=0;
  int breakloop=0;

  while(Serial.available() && (breakloop==0))
  {
    i=Serial.read();
    if((i>='1')&&(i<='6'))
      flags ^= (ZONE_1 >> (i-'1'));

    if((i=='r')||(i=='R'))
      flags ^= READY;
    if((i=='a')||(i=='A'))
      flags ^= ARMED;
    if((i=='m')||(i=='M'))
      flags ^= MEMORY;
    if((i=='b')||(i=='B'))
      flags ^= BYPASS;
    if((i=='t')||(i=='T'))
      flags ^= TROUBLE;
    if(i=='S')
    {
      flags |= BUZZER;
      buzzer_counter+=16;
      break;
    }
    if(i=='s')
    {
      flags |= BUZZER;
      buzzer_counter++;
      break;
    }
    if(i==' ')
      break;
  }
  if(buzzer_counter)
    buzzer_counter--;
  else
    flags &= ~BUZZER;

  i=readdata(flags ^ key_just_pressed);


  if(last_key_pressed==NO_KEY_PRESSED)
  {
    if(i != NO_KEY_PRESSED)
      Serial.print((char)(i));
  }
  if((last_key_pressed!=i)&&(last_key_pressed==NO_KEY_PRESSED))
    key_just_pressed=BUZZER;
  else
    key_just_pressed=NO_FLAGS;
  last_key_pressed=i;

  delayMicroseconds(3333);
}