What is 0xaa?
We know that 0xaa and 0x55 are hexa-decimal representation . Moreover each character in hexadecimal is represent using 4bits. so , 0xaa is equivalent to 1010 1010 (since, a = 1010 in binary) and 0x55 is equivalent to 0101 0101 (since, 5 = 0101 in binary)