Writing HIGH and LOW to output pins in Embedded C - Step-by-Step Execution

Concept Flow - Writing HIGH and LOW to output pins

Setup pin as OUTPUT

↓

Write HIGH to pin

→Pin voltage set to HIGH

↓

Write LOW to pin

→Pin voltage set to LOW

↓

End

First, configure the pin as an output. Then write HIGH or LOW to set the pin voltage accordingly.

Execution Sample

Embedded C

pinMode(13, OUTPUT);
digitalWrite(13, HIGH);
delay(1000);
digitalWrite(13, LOW);

Set pin 13 as output, turn it ON (HIGH), wait 1 second, then turn it OFF (LOW).

Execution Table

Step	Action	Pin Mode	Pin State	Output Voltage
1	pinMode(13, OUTPUT)	OUTPUT	LOW (default)	0V (LOW)
2	digitalWrite(13, HIGH)	OUTPUT	HIGH	5V (HIGH)
3	delay(1000)	OUTPUT	HIGH	5V (HIGH)
4	digitalWrite(13, LOW)	OUTPUT	LOW	0V (LOW)
5	End of code	OUTPUT	LOW	0V (LOW)

💡 Code ends after setting pin 13 LOW.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	Final
Pin 13 Mode	INPUT (default)	OUTPUT	OUTPUT	OUTPUT	OUTPUT	OUTPUT
Pin 13 State	LOW (default)	LOW	HIGH	HIGH	LOW	LOW
Pin 13 Voltage	0V (LOW)	0V (LOW)	5V (HIGH)	5V (HIGH)	0V (LOW)	0V (LOW)

Key Moments - 3 Insights

Why do we need to set the pin mode to OUTPUT before writing HIGH or LOW?

Because the pin must be configured as OUTPUT to control voltage levels; otherwise, writing HIGH or LOW won't change the pin voltage (see Step 1 in execution_table).

Does writing HIGH immediately change the pin voltage?

Yes, writing HIGH sets the pin voltage to 5V right away (Step 2 shows pin state changes to HIGH and voltage to 5V).

What happens if we write LOW after writing HIGH?

The pin voltage changes back to 0V (LOW), turning the output off (Step 4 shows this change).

Visual Quiz - 3 Questions

Look at the execution_table, what is the pin state after Step 2?

A LOW

B HIGH

C INPUT

D UNKNOWN

💡 Hint

Check the 'Pin State' column at Step 2 in the execution_table.

At which step does the pin voltage become 0V after being HIGH?

A Step 1

B Step 2

C Step 4

D Step 3

💡 Hint

Look at the 'Pin 13 Voltage' in variable_tracker after Step 4.

If we skip setting pinMode to OUTPUT, what will happen when writing HIGH?

A Pin voltage stays LOW

B Pin voltage changes to HIGH

C Pin mode automatically changes to OUTPUT

D Program crashes

💡 Hint

Refer to key_moments about why pinMode must be set before writing.

Concept Snapshot

pinMode(pin, OUTPUT) sets pin as output
Use digitalWrite(pin, HIGH) to set voltage HIGH (5V)
Use digitalWrite(pin, LOW) to set voltage LOW (0V)
Must set pinMode before writing
Writing changes pin voltage immediately
Delay can keep state before changing

Full Transcript

This example shows how to control an output pin in embedded C. First, the pin is set as OUTPUT using pinMode. Then digitalWrite sets the pin voltage HIGH or LOW. The execution table tracks each step: setting mode, writing HIGH, waiting, then writing LOW. Variables track pin mode, state, and voltage changes. Key moments clarify why setting pin mode is necessary and how writing changes voltage immediately. The visual quiz tests understanding of pin state and voltage changes at each step. The snapshot summarizes the commands and rules for writing HIGH and LOW to output pins.