#define KCL 1
#define KDA 0
#define CLK 3
#define DAT 4
#define WAIT 20

void setup()
{
  pinMode(KCL, OUTPUT);
  pinMode(KDA, INPUT);
  pinMode(CLK, OUTPUT);
  pinMode(DAT, OUTPUT);
  digitalWrite(KCL, LOW);
  digitalWrite(CLK, HIGH);
  delay(300);
}

void loop()
{
  uint8_t code;
  char buff[10];

  code = getKeycode();
  if(code != 0xFF)
  {
    sprintf(buff, "%02X", code);
    sendStr(buff);
  }
  delay(100);
}

uint8_t getKeycode()
{
  uint8_t val = 0;
  
  digitalWrite(KCL, HIGH); //スタートビット
  delay(WAIT);
  digitalWrite(KCL, LOW);
  delay(WAIT);

  for(int i=0; i<8; i++)
  {
    digitalWrite(KCL, HIGH);
    delay(WAIT);
    digitalWrite(KCL, LOW);
    val |= digitalRead(KDA) << i;
    delay(WAIT);
  }
  return val;
}

void sendStr(uint8_t* str)
{
  static int count = 0;
  uint8_t* p;

  p = str;
  while(*p != 0)
  {
    sendChar(*(p++));
    if(++count > 15)
    {
      sendChar(0x80); //カーソルを先頭へ
      count = 0;
    }
  }
}

void sendChar(uint8_t chr)
{
  for(int n = 0; n < 8; n++)
  {
    digitalWrite(DAT, (chr >> n) & 1);
    delayMicroseconds(WAIT);
    digitalWrite(CLK, LOW);
    delayMicroseconds(WAIT);
    digitalWrite(CLK, HIGH);
  }
}