GPIO port-wide operations in Embedded C - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to set all pins of GPIO port A as output.

Embedded C

GPIOA->MODER = [1];

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

A0x55555555

B0xAAAAAAAA

C0x00000000

D0xFFFFFFFF

Attempts:

3 left

💡 Hint

Common Mistakes

Using 0xFFFFFFFF sets all bits to '11' which is analog mode.

Using 0x00000000 sets all pins as input.

Each pin requires 2 bits in MODER. Setting all pins as output means setting each 2-bit pair to '01', which corresponds to 0x55555555.

2fill in blank

medium

Complete the code to write a high level to all pins of GPIO port B.

Embedded C

GPIOB->ODR = [1];

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

A0xAAAAAAAA

B0xFFFFFFFF

C0x00000000

D0x55555555

Attempts:

3 left

💡 Hint

Common Mistakes

Using 0x00000000 sets all pins low.

Using 0xAAAAAAAA sets alternating pins high and low.

Writing 0xFFFFFFFF sets all output pins to high (logic 1).

3fill in blank

hard

Fix the error in the code to toggle all pins of GPIO port C.

Embedded C

GPIOC->ODR = GPIOC->ODR [1] 0xFFFFFFFF;

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

A<<

B|

C&

D^

Attempts:

3 left

💡 Hint

Common Mistakes

Using '&' clears bits.

Using '|' sets bits but does not toggle.

Using '<<' is a shift operation, not toggle.

The XOR operator '^' toggles bits. XOR with 0xFFFFFFFF flips all bits in ODR.

4fill in blank

hard

Fill both blanks to configure GPIO port D pins as input with pull-up resistors enabled.

Embedded C

GPIOD->MODER = [1];
GPIOD->PUPDR = [2];

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

A0x00000000

B0x55555555

C0xAAAAAAAA

D0xFFFFFFFF

Attempts:

3 left

💡 Hint

Common Mistakes

Setting MODER to 0x55555555 configures pins as output, not input.

Setting PUPDR to 0xAAAAAAAA enables pull-down resistors, not pull-up.

Setting MODER to 0x00000000 configures all pins as input (00). Setting PUPDR to 0x55555555 enables pull-up resistors (01 for each pin).

5fill in blank

hard

Fill all three blanks to create a dictionary comprehension that maps each GPIO pin number to its output state if the pin number is greater than 4.

Embedded C

pin_states = [1]: GPIOE->ODR & (1 << [2]) != 0 for [3] in range(8) if [3] > 4

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

Apin

Di

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variable names causes syntax errors.

Not shifting 1 by the pin number causes wrong bit checking.

The comprehension maps each pin number (pin) to its output state by checking the bit in ODR shifted by pin. The variable iterates as 'pin' in range(8) and filters pins greater than 4.

Practice

1. What does writing a value to PORTB in embedded C typically do in GPIO port-wide operations?

easy

A. Configures the direction of pins in port B

B. Sets the output levels of all pins in port B at once

C. Reads the input levels of all pins in port B

D. Enables pull-up resistors on port B pins

Solution

1. Step 1: Understand PORT register role

   The PORT register controls the output voltage levels on the pins of a GPIO port.

2. Step 2: Effect of writing to PORTB

   Writing a value to PORTB sets the output state (high or low) of all pins in port B simultaneously.

3. Final Answer:

   Sets the output levels of all pins in port B at once -> Option B

4. Quick Check:

   PORTB write = set output levels [OK]

Hint: PORTx controls output levels of all pins together [OK]

Common Mistakes:

• Confusing PORT with DDR (direction register)
• Thinking PORT reads input levels
• Assuming PORT configures pull-ups

2. Which of the following is the correct syntax to set all pins of port D as outputs in embedded C?

easy

A. PINB = 0xFF;

B. PORTD = 0xFF;

C. DDRD = 0xFF;

D. DDRB = 0x00;

Solution

1. Step 1: Identify DDR register purpose

   DDRx registers set pin directions: 1 for output, 0 for input.

2. Step 2: Set all pins of port D as output

   Writing 0xFF (all bits 1) to DDRD sets all pins as outputs.

3. Final Answer:

   DDRD = 0xFF; -> Option C

4. Quick Check:

   DDRD = 0xFF sets all outputs [OK]

Hint: Use DDRx = 0xFF to set all pins output [OK]

Common Mistakes:

• Using PORTD instead of DDRD to set direction
• Writing to PINB which is read-only
• Setting DDRB instead of DDRD

3. Given the code snippet:

DDRC = 0x00;
PORTC = 0xFF;
uint8_t val = PINC;

What is the value of val assuming all pins on port C are externally connected to ground?

medium

A. 0x00

B. Undefined behavior

C. 0xFF with pull-ups disabled

D. 0xFF

Solution

1. Step 1: Analyze DDRC and PORTC settings

   DDRC = 0x00 sets all pins as inputs. PORTC = 0xFF enables pull-up resistors on all pins.

2. Step 2: Effect of external ground on input pins

   Even with pull-ups enabled, external ground forces pins low, so PINC reads 0x00.

3. Final Answer:

   0x00 -> Option A

4. Quick Check:

   Input pins grounded read 0x00 [OK]

Hint: Input pins grounded read zero despite pull-ups [OK]

Common Mistakes:

• Assuming pull-ups force input high regardless
• Confusing PORTC write with output level
• Ignoring DDRC input configuration

4. Identify the error in the following code snippet for setting port A pins as outputs and turning them all high:

DDRA = 0xFF;
PINA = 0xFF;

medium

A. PORTA should be used instead of PINA to set outputs

B. DDRA should be set to 0x00

C. PINA is not a valid register name

D. No error, code is correct

Solution

1. Step 1: Check register purpose

   PINA reads input levels or toggles outputs, but does not directly set output levels.

2. Step 2: Correct register to set output levels

   To set output pins high, write to PORTA, not PINx.

3. Final Answer:

   PORTA should be used instead of PINA to set outputs -> Option A

4. Quick Check:

   Use PORTA to write outputs, not PINx [OK]

Hint: Use PORTx to write outputs, PINx is for reading inputs [OK]

Common Mistakes:

• Using PINx registers instead of PORTx for outputs
• Writing outputs to PIN register
• Confusing DDR and PORT registers

5. You want to configure port C pins 0-3 as outputs and pins 4-7 as inputs with pull-ups enabled. Which code correctly achieves this?

hard

A. DDRC = 0x00; PORTC = 0xFF;

B. DDRC = 0xF0; PORTC = 0x0F;

C. DDRC = 0xFF; PORTC = 0x00;

D. DDRC = 0x0F; PORTC = 0xF0;

Solution

1. Step 1: Set pins 0-3 as outputs

   Bits 0-3 set to 1 in DDRC means DDRC = 0x0F (00001111 binary).

2. Step 2: Enable pull-ups on pins 4-7 inputs

   Pins 4-7 inputs require DDRC bits 4-7 = 0, and PORTC bits 4-7 = 1 to enable pull-ups, so PORTC = 0xF0.

3. Final Answer:

   DDRC = 0x0F; PORTC = 0xF0; -> Option D

4. Quick Check:

   Outputs low nibble, pull-ups high nibble [OK]

Hint: DDRx bits 1=output, PORTx bits 1=pull-up on inputs [OK]

Common Mistakes:

• Mixing up which bits control direction vs pull-ups
• Setting pull-ups on output pins
• Using wrong hex values for bit masks