Arduino - BitwiseCompoundOr

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## compound bitwise OR (|=)

#### Description

The compound bitwise OR operator (|=) is often used with a variable and a constant to "set" (set to 1) particular bits in a variable.

#### Syntax:

    x |= y;   // equivalent to x = x | y;

#### Parameters

x: a char, int or long variable
y: an integer constant or char, int, or long

#### Example:

First, a review of the Bitwise OR (|) operator

       0  0  1  1    operand1
       0  1  0  1    operand2
       ----------
       0  1  1  1    (operand1 | operand2) - returned result

Bits that are "bitwise ORed" with 0 are unchanged, so if myByte is a byte variable,
myByte | B00000000 = myByte;

Bits that are "bitwise ORed" with 1 are set to 1 so:
myByte | B11111111 = B11111111;

Consequently - to set bits 0 & 1 of a variable, while leaving the rest of the variable unchanged, use the compound bitwise OR operator (|=) with the constant B00000011

       1  0  1  0  1  0  1  0    variable
       0  0  0  0  0  0  1  1    mask
       ----------------------
       1  0  1  0  1  0  1  1

     variable unchanged
                         bits set

Here is the same representation with the variables bits replaced with the symbol x

       x  x  x  x  x  x  x  x    variable
       0  0  0  0  0  0  1  1    mask
       ----------------------
       x  x  x  x  x  x  1  1

     variable unchanged
                         bits set

So if:

    myByte =  B10101010;

    myByte |= B00000011 == B10101011;

See Also

- &= (compound bitwise and)
- & (bitwise and)
- | (bitwise or)

Reference Home

Corrections, suggestions, and new documentation should be posted to the Forum.

The text of the Arduino reference is licensed under a Creative Commons Attribution-ShareAlike 3.0 License. Code samples in the reference are released into the public domain.

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