📚 Bitwise Operations in C for Microcontroller Programming

Bitwise operations are essential for low-level programming, especially when working with microcontrollers and GPIO. They allow precise control over individual bits in registers.

🎯 Learning Objectives

By the end of this lesson, students should be able to:

• Itentify the Bitwise Operators and how they are used in the C language
• Understand how to SET, CLEAR, MASK, and TOGGLE a bit
• Successfully use bit-shifting for efficient code statements

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1️⃣ Core Bitwise Operators

Operator	Symbol	Description	Example
AND	&	Sets each bit to 1 if both bits are 1	5 & 3 = 1
OR	|	Sets each bit to 1 if at least one bit is 1	5 | 3 = 7
XOR	^	Sets each bit to 1 if only one bit is 1	5 ^ 3 = 6
NOT	~	Inverts all bits	~5 = -6
Left Shift	<<	Shifts bits left, filling with 0s	4 << 1 = 8
Right Shift	>>	Shifts bits right, discarding bits	4 >> 1 = 2

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2️⃣ Bit Manipulation Techniques

• These are commonly used to control GPIO pins or manage flags.
• Let’s pretend we want to control and monitor bits in an 8-bit register called GPIOA.

Objectives

• We want to be able to write one specific bit as “0” or “1’” without modifying the rest
• We want to be able to read one specific bit to know if is either “1” or “0”

GPIOA

Bit 7	Bit 6	Bit 5	Bit 4	Bit 3	Bit 2	Bit 1	Bit 0
0	0	0	0	0	0	0	0

Terminology

• Writing a “1” to a specific bit leaving the rest intact is called SET
• Writing a “0” to a specific bit leaving the rest intact is called CLEAR

• Checking the status of a bit to know if itg’s either “1” or “0” is called BIT MASKING

• Assuming we have previously defined this mask:

const uint8_t BIT5 = 0b00100000; // and 8-bit mask that has a "1" only in b5

3️⃣ Relevant Manipulation Operations

✅ Set a Bit (write a 1)

Turn ON a specific bit using OR:

GPIOA |= BIT5;  // Set BIT5, GPIOA = GPIOA | BIT5 

❌ Clear a Bit (write a 0)

Turn OFF a specific bit using AND with NOT

GPIOA &= ~BIT5;  // Clear BIT5, GPIOA = GPIOA & ~BIT5 

🔁 Toggle a Bit (chanmge 1 to 0 and vice-versa)

Flip the state of a bit using XOR:

GPIOA ^= BIT5;  // Toggle BIT5, GPIOA = GPIOA ^ BIT5 

🔍 Mask a Bit (test a bit)

Check if a bit is HIGH using AND:

if (GPIOA & BIT5) 
{//BIT5 is HIGH (1)  
    
    //Do something

}
else
{//BIT5 is LOW (0)
    
    //Do something

}

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4️⃣ Shift Operations

Left Shift (<<)

uint8_t mask = 1 << 5;  // Creates 0b00100000

//Example
const uint8_t FLAG_READY  (1 << 0) //0b00000001
const uint8_t FLAG_ERROR  (1 << 1) //0b00000010

uint8_t status = 0;     //variable to check status
status |= FLAG_READY;   //SET FLAG_READY bit
status &= ~FLAG_ERROR;  //CLEAR FLAG_ERROR bit
if (status & FLAG_READY) 
{//Flag ready is SET
    // Proceed with operation
}

🎯Practical Activity

• Using the virtual console on Segger create a simple program that reads a positive integer from the console and saves it into a 16-bit unsigned int variable
• Using bit-tmasking and bit-shifting operations display the number in binary (16-bit) on the debug console
• Remember to read a number from the virtual console you need to use ‘scanf’ and to print it ‘printf’ with the proper string formatter.