Configuring pin as input or output in Embedded C - Practice Exercises

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this pin configuration code?

Consider a microcontroller where setting a bit in the DDR (Data Direction Register) configures the pin as output (1) or input (0). What will be the value of DDRB after running this code?

Embedded C

DDRB = 0x00;
DDRB |= (1 << 3);  // Set pin 3 as output
DDRB &= ~(1 << 1); // Set pin 1 as input

A 0x0A

B 0x08

C 0x0C

D 0x02

💡 Hint

Remember that (1 << 3) sets bit 3 and (1 << 1) sets bit 1. |= sets bits, &=~ clears bits.

Initially DDRB is 0x00 (all pins input). Setting bit 3 (pin 3) to 1 makes it output. Clearing bit 1 keeps it input. So only bit 3 is set, which is 0x08 in hex.

🧠 Conceptual

intermediate

Which statement correctly configures pin 5 as input?

Given a DDR register controlling pin directions, which code snippet correctly sets pin 5 as input without changing other pins?

A DDR &= ~(1 << 5);

B DDR = (1 << 5);

C DDR |= (1 << 5);

D DDR ^= (1 << 5);

💡 Hint

Input pins have DDR bit cleared (0). Use bitwise AND with NOT to clear a bit.

To set pin 5 as input, clear bit 5 in DDR. DDR &= ~(1 << 5) clears bit 5 and keeps others unchanged.

🔧 Debug

advanced

Why does this code fail to configure pin 2 as output?

This code is intended to set pin 2 as output by setting bit 2 in DDR. Why does it not work as expected? DDRB = 0; DDRB & (1 << 2);

A DDRB is reset to 0 after setting the bit.

B The bit shift is incorrect; it should be (1 << 3).

C The code uses & instead of |=, so it does not set the bit.

D Pin 2 cannot be configured as output on this microcontroller.

💡 Hint

Check the operator used to set bits.

Using & does not set bits; it performs bitwise AND. To set a bit, use |= operator.

📝 Syntax

advanced

Which option contains a syntax error in configuring pin 0 as output?

Identify the code snippet that will cause a syntax error when trying to set pin 0 as output.

A DDRB |= (1 << 0);

B DDRB = DDRB | (1 << 0);

C DDRB |= 1 << 0;

D DDRB |= (1 << 0

💡 Hint

Look for missing parentheses or incomplete expressions.

Option D is missing a closing parenthesis, causing a syntax error.

🚀 Application

expert

How many pins are configured as output after this code runs?

Given DDRC initially 0x00, what is the number of pins configured as output after running this code? DDRC |= (1 << 0); DDRC |= (1 << 2); DDRC &= ~(1 << 0); DDRC |= (1 << 7);

A 2

B 3

C 1

D 4

💡 Hint

Count bits set to 1 in DDRC after all operations.

Pin 0 is first set then cleared (input). Pins 2 and 7 are set as output. So total 2 pins output.