Writing to a hardware register in Embedded C - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to write the value 0xFF to the hardware register.

Embedded C

volatile uint8_t *reg = (volatile uint8_t *)0x4000;
*reg = [1];

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

A255

B0x0F

C0x00

D0xFF

Attempts:

3 left

💡 Hint

Common Mistakes

Using 0x00 which clears the register instead of setting it.

Using decimal 255 without 0x prefix which is valid but less common in embedded C.

The value 0xFF is the correct hexadecimal value to write all bits set to 1 in an 8-bit register.

2fill in blank

medium

Complete the code to set bit 3 of the hardware register without changing other bits.

Embedded C

volatile uint8_t *reg = (volatile uint8_t *)0x4000;
*reg |= [1];

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

A0x08

B0x04

C0x10

D0x01

Attempts:

3 left

💡 Hint

Common Mistakes

Using 0x04 which sets bit 2 instead of bit 3.

Using 0x10 which sets bit 4 instead of bit 3.

Bit 3 corresponds to the value 0x08 (binary 00001000). Using bitwise OR sets this bit without affecting others.

3fill in blank

hard

Fix the error in the code to clear bit 2 of the hardware register without changing other bits.

Embedded C

volatile uint8_t *reg = (volatile uint8_t *)0x4000;
*reg &= [1];

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

A0x02

B0x04

C~0x04

D~0x02

Attempts:

3 left

💡 Hint

Common Mistakes

Using 0x04 which would keep only bit 2 and clear others.

Using ~0x02 which clears bit 1 instead of bit 2.

To clear bit 2 (value 0x04), use bitwise AND with the complement of 0x04 (~0x04). This clears bit 2 and keeps others unchanged.

4fill in blank

hard

Fill both blanks to toggle bit 1 of the hardware register using XOR.

Embedded C

volatile uint8_t *reg = (volatile uint8_t *)0x4000;
*reg [1]= [2];

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

A^

B|

C0x02

D0x01

Attempts:

3 left

💡 Hint

Common Mistakes

Using OR (|) instead of XOR (^) which only sets bits.

Using 0x01 which toggles bit 0 instead of bit 1.

Using XOR (^) with 0x02 toggles bit 1 without affecting other bits.

5fill in blank

hard

Fill all three blanks to write the value 0xAA to the register, then clear bit 7 and set bit 0.

Embedded C

volatile uint8_t *reg = (volatile uint8_t *)0x4000;
*reg = [1];
*reg &= [2];
*reg |= [3];

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

A0xAA

B~0x80

C0x01

D0xFF

Attempts:

3 left

💡 Hint

Common Mistakes

Using 0xFF instead of 0xAA as initial value.

Using 0x80 instead of ~0x80 to clear bit 7.

Using 0x02 instead of 0x01 to set bit 0.

First, write 0xAA to the register. Then clear bit 7 by ANDing with ~0x80. Finally, set bit 0 by ORing with 0x01.