The compound bitwise AND operator (&=) is often used with a variable and a constant to force particular bits in a variable to the LOW state (to 0). This is often referred to in programming guides as "clearing" or "resetting" bits.
x &= y; // equivalent to x = x & y;
x
a char, int or long variable
y
an integer constant or char, int, or long
First, a review of the Bitwise AND (&) operator
0 0 1 1 operand1
0 1 0 1 operand2
----------
0 0 0 1 (operand1 & operand2) - returned result
Bits that are "bitwise ANDed" with 0 are cleared to 0 so, if myByte is a byte variable
myByte & B00000000 = 0;
Bits that are "bitwise ANDed" with 1 are unchanged so,
myByte & B11111111 = myByte;