Writing HIGH and LOW to output pins in Embedded C - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does writing HIGH to an output pin mean in embedded C?

Writing HIGH sets the output pin voltage to a high level, usually 5V or 3.3V, turning the pin ON or activating connected devices like LEDs.

beginner

How do you write LOW to an output pin in embedded C?

You write LOW by setting the pin's output register to 0, which sets the pin voltage to 0V, turning the pin OFF or deactivating connected devices.

beginner

Which function is commonly used to set a pin HIGH or LOW in Arduino (embedded C)?

The function digitalWrite(pin, value) is used, where value can be HIGH or LOW to set the pin voltage accordingly.

beginner

Why must a pin be set as OUTPUT before writing HIGH or LOW?

Pins default to input mode. Setting a pin as OUTPUT configures it to send voltage signals, allowing you to write HIGH or LOW to control devices.

intermediate

What happens if you write HIGH to a pin configured as INPUT?

Writing HIGH to an INPUT pin usually enables the internal pull-up resistor, but does not drive the pin voltage high externally; the pin reads signals instead of sending them.

What voltage level does writing HIGH to an output pin usually set?

A 12V

B 0V

C It depends on the input signal

D 5V or 3.3V

Writing HIGH sets the pin voltage to the board's logic high level, typically 5V or 3.3V.

Which function sets a pin as output in Arduino embedded C?

A digitalWrite(pin, OUTPUT)

B pinMode(pin, OUTPUT)

C setPin(pin, OUTPUT)

D writePin(pin, OUTPUT)

pinMode(pin, OUTPUT) configures the pin to output mode.

What does digitalWrite(pin, LOW) do?

A Sets the pin voltage to 0V

B Sets the pin voltage to 5V

C Reads the pin voltage

D Configures the pin as input

digitalWrite(pin, LOW) sets the pin voltage to 0 volts.

If a pin is not set as OUTPUT, what happens when you write HIGH to it?

A No voltage is driven on the pin

B Pin voltage goes to 5V

C Pin voltage goes to 0V

D Pin mode changes to OUTPUT automatically

Pins not set as OUTPUT do not drive voltage even if you write HIGH.

Which of these is the correct way to turn on an LED connected to pin 13?

A pinMode(13, INPUT); digitalWrite(13, HIGH);

B digitalWrite(13, HIGH); pinMode(13, OUTPUT);

C pinMode(13, OUTPUT); digitalWrite(13, HIGH);

D digitalWrite(13, LOW); pinMode(13, OUTPUT);

You must set pin 13 as OUTPUT before writing HIGH to turn on the LED.

Explain how to turn an output pin HIGH and LOW in embedded C and why setting pin mode matters.

Think about configuring the pin first, then sending voltage signals.

Describe what happens if you try to write HIGH to a pin that is set as INPUT.

Consider the difference between input and output pin modes.