LED display timer for Arduino

Sketch.ino

// 参考: http://garretlab.web.fc2.com/arduino/introduction/beginning_with_7segment_led/

int num[10][8] = {
  {0, 0, 1, 0, 1, 0, 0, 0}, // 0
  {1, 1, 1, 0, 1, 0, 1, 1}, // 1
  {0, 0, 1, 1, 0, 0, 1, 0}, // 2
  {1, 0, 1, 0, 0, 0, 1, 0}, // 3
  {1, 1, 1, 0, 0, 0, 0, 1}, // 4
  {1, 0, 1, 0, 0, 1, 0, 0}, // 5
  {0, 0, 1, 0, 0, 1, 0, 0}, // 6
  {1, 1, 1, 0, 1, 0, 0, 0}, // 7
  {0, 0, 1, 0, 0, 0, 0, 0}, // 8
  {1, 0, 1, 0, 0, 0, 0, 0}  // 9
};

int count =  0;

void setup() {
  // put your setup code here, to run once:
  for (int i = 2; i <= 13; i++) {
    pinMode(i, OUTPUT);
  }
  
  OCR2A = 255;
  TCCR2B = 0b100;
  bitWrite(TIMSK2, OCIE2A, 1);
}

void loop() {
  // put your main code here, to run repeatedly:
  delay(1000);
  
  count += 1;
  
  if (10000 <= count) {
    count = 0;
  }
}

// 数字を全てクリアする
void clearNumbers() {
  for (int i = 0; i < 8; i++) {
    int pinNo = i + 6;
    digitalWrite(pinNo, HIGH);
  }  
}

// 複数桁の数字を表示する
void showNumbers(int count) {
  int n = count;
  for (int i = 0; i < 4; i++) {
    digitalWrite(i + 2, LOW);  
    showNumber(n % 10);
    delayMicroseconds(100);
    clearNumbers();
    digitalWrite(i + 2, HIGH); 
    n = n / 10;
  }
}

// 1桁の数字を表示する
void showNumber(int n) {
  // LED show
  for (int i = 0; i < 8; i++) {
    int pinNo = i + 6;
    digitalWrite(pinNo, num[n][i]);
  }
}

// 割り込み
ISR(TIMER2_COMPA_vect) {
  showNumbers(count);
}