// 16-bit integer (s) = byte-by-byte (c[0], c[1])
//
union { short s; char c[2]; } u;

void setup() {
  Serial1.begin(9600, SERIAL_8E1);
  u.s = 27099; // 0x69db
}

void loop() {
  Serial1.write(u.c[0]); Serial1.write(u.c[1]);
  delay(10);
}