How Arduino code maps to AVR hardware - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to set pin 13 as an output in Arduino.

Arduino

void setup() {
  pinMode([1], OUTPUT);
}

void loop() {
  // your code here
}

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

A11

B12

C10

D13

Attempts:

3 left

💡 Hint

Common Mistakes

Using a pin number that does not correspond to the built-in LED.

Forgetting to set the pin mode before using it.

Pin 13 is commonly used as the built-in LED pin on Arduino boards and must be set as output to control it.

2fill in blank

medium

Complete the code to turn the LED on connected to pin 13.

Arduino

void loop() {
  digitalWrite([1], HIGH);
  delay(1000);
  digitalWrite(13, LOW);
  delay(1000);
}

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

A12

B11

C13

D10

Attempts:

3 left

💡 Hint

Common Mistakes

Writing HIGH to the wrong pin number.

Not matching the pin number used in pinMode.

To turn on the LED connected to pin 13, you must write HIGH to pin 13.

3fill in blank

hard

Fix the error in the code to correctly toggle the LED on pin 13.

Arduino

void loop() {
  digitalWrite(13, [1]);
  delay(500);
  digitalWrite(13, LOW);
  delay(500);
}

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

AHIGH

BLOW

CON

DTRUE

Attempts:

3 left

💡 Hint

Common Mistakes

Using ON or TRUE instead of HIGH.

Confusing digitalWrite values with boolean values.

To turn the LED on, you must write HIGH to the pin. ON and TRUE are not valid values for digitalWrite.

4fill in blank

hard

Fill both blanks to create a dictionary mapping pin numbers to their states for pins 12 and 13.

Arduino

int pinStates[] = { [1], [2] };

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

A12

B13

CHIGH

DLOW

Attempts:

3 left

💡 Hint

Common Mistakes

Using HIGH or LOW instead of pin numbers.

Mixing pin numbers and states in the same array.

The array holds pin numbers 12 and 13 to track their states.

5fill in blank

hard

Fill all three blanks to read the state of pin 13 and store it in a variable.

Arduino

int ledState = digitalRead([1]);
if (ledState == [2]) {
  digitalWrite([3], LOW);
}

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

A13

BHIGH

DLOW

Attempts:

3 left

💡 Hint

Common Mistakes

Using different pin numbers for reading and writing.

Comparing to LOW instead of HIGH.

Read pin 13 state, check if it is HIGH, then turn it LOW.

Practice

1. What does the Arduino digitalWrite() function do in relation to the AVR hardware?

easy

A. It sets a specific pin on the AVR chip to HIGH or LOW voltage.

B. It reads the voltage level from a pin on the AVR chip.

C. It configures the clock speed of the AVR chip.

D. It resets the AVR chip to its initial state.

Solution

1. Step 1: Understand the purpose of digitalWrite()

   The digitalWrite() function is used to control output pins on the Arduino board.

2. Step 2: Map function to AVR hardware action

   It changes the voltage level on a specific pin of the AVR chip to either HIGH (5V) or LOW (0V).

3. Final Answer:

   It sets a specific pin on the AVR chip to HIGH or LOW voltage. -> Option A

4. Quick Check:

   digitalWrite() controls pin voltage = D [OK]

Hint: digitalWrite sets pin voltage HIGH or LOW [OK]

Common Mistakes:

• Confusing digitalWrite() with digitalRead()
• Thinking it resets the chip
• Assuming it changes clock speed

2. Which of the following is the correct syntax to set pin 13 as an output in Arduino code?

easy

A. pinMode(OUTPUT, 13);

B. pinMode(13, OUTPUT);

C. digitalWrite(13, OUTPUT);

D. digitalRead(13, OUTPUT);

Solution

1. Step 1: Identify correct function and parameters for pin mode

   The function to set pin mode is pinMode(), which takes the pin number first, then the mode.

2. Step 2: Match correct parameter order

   The correct order is pinMode(pin, mode); so pinMode(13, OUTPUT); is correct.

3. Final Answer:

   pinMode(13, OUTPUT); -> Option B

4. Quick Check:

   pinMode(pin, mode) sets pin direction = A [OK]

Hint: pinMode(pin, OUTPUT) sets pin as output [OK]

Common Mistakes:

• Swapping parameters in pinMode()
• Using digitalWrite() to set pin mode
• Using digitalRead() incorrectly

3. Consider this Arduino code snippet:

pinMode(8, OUTPUT);
digitalWrite(8, HIGH);
int val = digitalRead(8);

What will be the value of val after running this code?

medium

A. Undefined behavior

B. 0

C. 1

D. Compilation error

Solution

1. Step 1: Analyze pin mode and write operations

   Pin 8 is set as OUTPUT and then set to HIGH voltage.

2. Step 2: Understand digitalRead() on an OUTPUT pin

   Reading a pin set as OUTPUT returns the value last set by digitalWrite() since PIN register reflects the output pin voltage, which is HIGH (1).

3. Final Answer:

   1 -> Option C

4. Quick Check:

   digitalRead() on OUTPUT pin returns 1 = A [OK]

Hint: digitalRead on OUTPUT pin returns the written value (1) [OK]

Common Mistakes:

• Assuming digitalRead returns 0 on output pin
• Thinking digitalRead cannot read output pins
• Thinking code causes error

4. This Arduino code is intended to blink an LED on pin 13, but it doesn't work:

void setup() {
  digitalWrite(13, HIGH);
  pinMode(13, OUTPUT);
}
void loop() {
  digitalWrite(13, LOW);
  delay(1000);
  digitalWrite(13, HIGH);
  delay(1000);
}

What is the main problem?

medium

A. digitalWrite() cannot be used on pin 13

B. delay() cannot be used in loop()

C. setup() function is missing

D. pinMode() must be called before digitalWrite() in setup()

Solution

1. Step 1: Check order of pin setup in setup()

   Pin mode must be set before writing to the pin to ensure proper hardware configuration.

2. Step 2: Identify incorrect sequence

   The code calls digitalWrite(13, HIGH); before pinMode(13, OUTPUT);, which can cause the pin not to behave as expected.

3. Final Answer:

   pinMode() must be called before digitalWrite() in setup() -> Option D

4. Quick Check:

   Set pinMode before digitalWrite = C [OK]

Hint: Always set pinMode before digitalWrite [OK]

Common Mistakes:

• Calling digitalWrite before pinMode
• Thinking delay() is invalid
• Assuming pin 13 is special and can't be used

5. You want to toggle an LED connected to pin 7 every 500ms using direct AVR port manipulation for speed. Which code snippet correctly maps Arduino pin 7 to AVR PORTD and toggles it?

hard

A. DDRD |= (1 << DDD6); PORTD ^= (1 << PORTD6);

B. DDRB |= (1 << DDB7); PORTB ^= (1 << PORTB7);

C. DDRC |= (1 << DDC7); PORTC ^= (1 << PORTC7);

D. DDRD |= (1 << DDD7); PORTD ^= (1 << PD7);

Solution

1. Step 1: Identify Arduino pin 7 AVR port and bit

   On Arduino Uno, pin 7 maps to PORTD bit 6 (PD6), not bit 7.

2. Step 2: Set pin 7 as output and toggle it

   Setting DDRD bit 6 to 1 configures pin 7 as output. Toggling PORTD bit 6 flips the pin state.

3. Final Answer:

   DDRD |= (1 << DDD6); PORTD ^= (1 << PORTD6); -> Option A

4. Quick Check:

   Pin 7 = PD6 toggle = D [OK]

Hint: Pin 7 is PD6; set DDRD and toggle PORTD bit 6 [OK]

Common Mistakes:

• Using wrong port (PORTB or PORTC) for pin 7
• Setting wrong bit number
• Confusing DDRx and PORTx registers