LED control patterns in Embedded C - Step-by-Step Execution

Concept Flow - LED control patterns

Start

↓

Initialize LEDs

↓

Set pattern index = 0

↓

Loop Start

↓

Turn ON LEDs according to pattern

↓

Delay for visibility

↓

Turn OFF LEDs

↓

Increment pattern index

↓

Check if pattern index < total patterns?

No→End

↩Back to Loop Start

The program initializes LEDs, then loops through different LED patterns turning them on and off with delays, cycling through all patterns before stopping.

Execution Sample

Embedded C

int patterns[] = {0x01, 0x02, 0x04};
int i = 0;
while(i < 3) {
  LED_PORT = patterns[i];
  delay();
  LED_PORT = 0;
  delay();
  i++;
}

This code cycles through three LED patterns turning each on and off with a delay.

Execution Table

Step	i	LED_PORT value (hex)	Action	Output
1	0	0x01	Turn ON first LED pattern	LED1 ON
2	0	0x00	Turn OFF LEDs	All LEDs OFF
3	1	0x02	Turn ON second LED pattern	LED2 ON
4	1	0x00	Turn OFF LEDs	All LEDs OFF
5	2	0x04	Turn ON third LED pattern	LED3 ON
6	2	0x00	Turn OFF LEDs	All LEDs OFF
7	3	-	Check loop condition i<3	Condition false, exit loop

💡 i reaches 3, condition i<3 is false, loop ends

Variable Tracker

Variable	Start	After Step 2	After Step 4	After Step 6	Final
i	0	1	2	3	3
LED_PORT	0x00	0x00	0x00	0x00	0x00

Key Moments - 3 Insights

Why does LED_PORT get set to 0 after each pattern?

Setting LED_PORT to 0 turns off all LEDs before the next pattern, as shown in steps 2, 4, and 6 in the execution_table.

What happens when i equals 3 in the loop?

At step 7, the condition i<3 is false, so the loop stops running, ending the LED pattern sequence.

Why do we increment i after turning LEDs off?

Incrementing i after turning LEDs off ensures the next pattern is selected in the next loop cycle, as seen between steps 2 and 3.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of LED_PORT at step 3?

A 0x00

B 0x01

C 0x02

D 0x04

💡 Hint

Check the LED_PORT value column at step 3 in the execution_table.

At which step does the loop condition become false?

A Step 7

B Step 6

C Step 3

D Step 1

💡 Hint

Look at the last row in the execution_table where the condition is checked.

If we add a fourth pattern 0x08, how many times will the loop run?

A 3 times

B 4 times

C 5 times

D 2 times

💡 Hint

Refer to variable_tracker for i increments and loop condition in execution_table.

Concept Snapshot

LED control patterns use arrays to store LED states.
Loop through each pattern, turn LEDs ON, delay, then OFF.
Increment index to move to next pattern.
Stop when all patterns are shown.
Use hex values to represent LEDs ON/OFF.

Full Transcript

This lesson shows how to control LEDs in patterns using embedded C. The program starts by initializing an array of LED patterns. It uses a loop to turn LEDs on according to each pattern, waits for a delay, then turns LEDs off. The index variable i tracks which pattern is active. After each pattern, i increments. When i reaches the number of patterns, the loop ends. The execution table traces each step, showing LED_PORT values and actions. Key moments clarify why LEDs turn off between patterns and when the loop stops. The quiz tests understanding of LED_PORT values, loop exit, and adding patterns. The snapshot summarizes the pattern control process simply.