#include <Keypad.h>

const uint8_t ROWS = 4;
const uint8_t COLS = 8;
char keys[ROWS][COLS] = {
  { 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H' },
  { 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P' },
  { 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X' },
  { 'Y', 'Z', '1', '2', '3', '4', '5', '6' }
};

uint8_t colPins[COLS] = { 9, 8, 7, 6, 5, 4, 3, 2};
uint8_t rowPins[ROWS] = {A3, A2, A1, A0};

Keypad keypad = Keypad(makeKeymap(keys), rowPins, colPins, ROWS, COLS);

void setup() {
  Serial.begin(9600);
}

void loop() {
  static byte cnt = 0;
  char key = keypad.getKey();

  if (key != NO_KEY) {
    Serial.write(key);
    if (++cnt >= 8) {
      cnt = 0;
      Serial.println();
    }
  }
}