AND for masking bits in Embedded C - Step-by-Step Execution

Concept Flow - AND for masking bits

Start with number

↓

Apply AND mask

↓

Result keeps bits where mask=1

↓

Result clears bits where mask=0

↓

Use result as needed

↓

End

This flow shows how applying an AND mask keeps certain bits and clears others in a number.

Execution Sample

Embedded C

unsigned char num = 0b11010110;
unsigned char mask = 0b00001111;
unsigned char result = num & mask;
// result keeps lower 4 bits of num

This code uses AND to keep only the lower 4 bits of num, clearing the upper bits.

Execution Table

Step	num (binary)	mask (binary)	Operation	Result (binary)	Result (decimal)
1	11010110	00001111	num & mask	00000110	6
2	N/A	N/A	Use result	00000110	6

💡 Finished applying AND mask; bits where mask=0 are cleared.

Variable Tracker

Variable	Start	After AND	Final
num	11010110 (214)	11010110 (214)	11010110 (214)
mask	00001111 (15)	00001111 (15)	00001111 (15)
result	N/A	00000110 (6)	00000110 (6)

Key Moments - 2 Insights

Why does the result only keep some bits of num?

Because AND with mask keeps bits only where mask has 1s (see execution_table step 1). Bits where mask is 0 become 0 in result.

What happens if mask is all zeros?

Result will be zero because AND with 0 clears all bits (not shown here but follows same logic).

Visual Quiz - 3 Questions

Look at the execution_table step 1, what is the decimal value of the result?

A 214

B 6

C 15

D 110

💡 Hint

Check the 'Result (decimal)' column in execution_table step 1.

At which step does the AND operation happen?

A Step 1

B Before Step 1

C Step 2

D No AND operation

💡 Hint

Look at the 'Operation' column in execution_table.

If mask was 0b11110000 instead, what bits of num would be kept?

A All bits

B Lower 4 bits

C Upper 4 bits

D No bits

💡 Hint

Mask bits with 1 keep those bits in num (see concept_flow).

Concept Snapshot

AND for masking bits:
- Use & operator between number and mask
- Bits where mask=1 stay same
- Bits where mask=0 become 0
- Useful to extract or clear bits
- Example: result = num & mask;

Full Transcript

This example shows how to use the AND operator to mask bits in embedded C. We start with a number and a mask. The mask has 1s where we want to keep bits and 0s where we want to clear bits. Applying AND between the number and mask keeps bits where mask is 1 and clears others. For example, num = 0b11010110 and mask = 0b00001111 results in 0b00000110, keeping only the lower 4 bits. This technique is useful to extract parts of a number or clear unwanted bits.