void setup() {
  // put your setup code here, to run once:
  volatile long i;
  volatile char *dir_f, *dir_k, *dir_a, *dir_c, row;
  volatile char *output_f, *input_k, *output_a, *output_c;

  // direction setup
  dir_f = 0x30; dir_k = 0x107;
  dir_a = 0x21; dir_c = 0x27;

  // I/O setup
  output_f = 0x31; input_k = 0x106;
  output_a = 0x22; output_c = 0x28;

  // enable pins for I/O
  *dir_f = 0x0F; *dir_k = 0x00;
  // *output_a = 0x0F; *output_c = 0x0F; test for 8 LEDS on

  while (1) {
    for (row = 0; row < 4; row++) {
      *output_f = 1 << row;
      *output_a = *input_k;
      
      if (*input_k != 0) {
        *output_c = 1 << row;
        for (i = 0; i < 200000; i++);
        *output_c = 0;
      }
    }
  }

  
}

void loop() {
  // put your main code here, to run repeatedly:

}