How to Use Bitwise OR in Embedded C: Syntax and Examples

In Embedded C, use the | operator to perform a bitwise OR between two integers. This operator compares each bit of the operands and sets the result bit to 1 if either bit is 1, otherwise 0. It is commonly used to set specific bits in hardware registers.

Syntax

The bitwise OR operator in Embedded C is represented by |. It takes two integer operands and compares their bits one by one.

• operand1 | operand2: Performs bitwise OR on each bit.
• Each bit in the result is 1 if either corresponding bit in operand1 or operand2 is 1.
• Used to combine flags or set bits without changing others.

c

result = operand1 | operand2;

Example

This example shows how to use bitwise OR to set specific bits in a variable, which is common in embedded programming to control hardware registers.

c

#include <stdio.h>

int main() {
    unsigned char reg = 0x12;  // Binary: 00010010
    unsigned char mask = 0x05; // Binary: 00000101

    // Set bits in reg using bitwise OR
    reg = reg | mask;

    printf("Result after OR: 0x%02X\n", reg);
    return 0;
}

Output

Result after OR: 0x17

Common Pitfalls

Common mistakes when using bitwise OR include:

• Using logical OR || instead of bitwise OR |, which works differently.
• Not using unsigned types, which can cause unexpected sign extension.
• Forgetting to assign the result back to a variable, since bitwise OR does not modify operands in place.

c

#include <stdio.h>

int main() {
    unsigned char reg = 0x12;
    unsigned char mask = 0x05;

    // Wrong: using logical OR (||) instead of bitwise OR (|)
    unsigned char wrong = reg || mask; // This will be 1 or 0, not bitwise OR

    // Correct:
    unsigned char correct = reg | mask;

    printf("Wrong result: 0x%02X\n", wrong);
    printf("Correct result: 0x%02X\n", correct);
    return 0;
}

Output

Wrong result: 0x01
Correct result: 0x17

Quick Reference

Operator	Description	Example	Result
|	Bitwise OR	0x12 | 0x05	0x17
||	Logical OR (not bitwise)	0x12 || 0x05	1
&	Bitwise AND	0x12 & 0x05	0x00
^	Bitwise XOR	0x12 ^ 0x05	0x17

Key Takeaways

Use the | operator to perform bitwise OR between two integers in Embedded C.

Bitwise OR sets bits to 1 if either operand bit is 1, useful for setting flags.

Avoid confusing bitwise OR (|) with logical OR (||), which behaves differently.

Always assign the result of bitwise OR to a variable; it does not change operands directly.

Use unsigned types to prevent unexpected behavior with bitwise operations.