Clearing a specific bit in a register in Embedded C - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to clear bit 3 of the variable reg.

Embedded C

reg = reg & [1];

Drag options to blanks, or click blank then click option'

A1 << 3

B1 >> 3

C~(1 >> 3)

D~(1 << 3)

Attempts:

3 left

💡 Hint

Common Mistakes

Using bitwise OR instead of AND.

Not inverting the mask before AND.

Shifting bits in the wrong direction.

To clear bit 3, we use bitwise AND with the complement of (1 shifted left by 3).

2fill in blank

medium

Complete the code to clear the bit specified by bit_pos in reg.

Embedded C

reg &= [1];

Drag options to blanks, or click blank then click option'

A~(1 << bit_pos)

B~(1 >> bit_pos)

C1 >> bit_pos

D1 << bit_pos

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting to invert the mask.

Using OR instead of AND.

Shifting bits in the wrong direction.

To clear a bit at position bit_pos, AND with the complement of (1 shifted left by bit_pos).

3fill in blank

hard

Fix the error in the code that attempts to clear bit 2 of reg.

Embedded C

reg = reg & [1];

Drag options to blanks, or click blank then click option'

A1 << 2

B~(1 << 2)

C~(1 >> 2)

D1 >> 2

Attempts:

3 left

💡 Hint

Common Mistakes

Using a mask without inversion.

Shifting bits right instead of left.

Using OR instead of AND.

The mask must be the complement of (1 shifted left by 2) to clear bit 2 correctly.

4fill in blank

hard

Fill both blanks to clear bit 5 in reg using a mask.

Embedded C

unsigned int mask = [1];
reg = reg & [2];

Drag options to blanks, or click blank then click option'

A~(1 << 5)

B1 << 5

Cmask

D~mask

Attempts:

3 left

💡 Hint

Common Mistakes

Not inverting the mask before AND.

Using the mask directly without inversion.

Shifting bits in the wrong direction.

Create the mask by shifting 1 left by 5, then clear bit 5 by ANDing reg with the complement of the mask.

5fill in blank

hard

Fill all three blanks to clear the bit at position pos in reg using a mask variable.

Embedded C

unsigned int mask = [1];
unsigned int inv_mask = [2];
reg = reg [3] inv_mask;

Drag options to blanks, or click blank then click option'

A1 << pos

B~mask

C&

D|

Attempts:

3 left

💡 Hint

Common Mistakes

Using OR instead of AND to clear the bit.

Not inverting the mask before AND.

Shifting bits right instead of left.

Create the mask by shifting 1 left by pos, invert it to get inv_mask, then clear the bit by ANDing reg with inv_mask.