EEPROM read and write in Arduino - Step-by-Step Execution

Concept Flow - EEPROM read and write

Start

↓

Write data to EEPROM

↓

Read data from EEPROM

↓

Use or display data

↓

End

This flow shows writing data to EEPROM, then reading it back to use or display.

Execution Sample

Arduino

#include <EEPROM.h>

void setup() {
  Serial.begin(9600);
  EEPROM.write(0, 42);
  int val = EEPROM.read(0);
  Serial.println(val);
}

void loop() {}

Writes 42 to EEPROM address 0, reads it back, and prints it to serial.

Execution Table

Step	Action	Address	Value Written	Value Read	Output
1	Write to EEPROM	0	42
2	Read from EEPROM	0		42
3	Print value				42
4	End				Execution stops

💡 Program ends after printing the EEPROM value.

Variable Tracker

Variable	Start	After Write	After Read	Final
EEPROM[0]	unknown	42	42	42
val	undefined	undefined	42	42

Key Moments - 3 Insights

Why do we write to EEPROM before reading?

Because EEPROM stores data persistently, we must write data first to have something to read back, as shown in steps 1 and 2 of the execution table.

What happens if we read from an EEPROM address that was never written?

The value read may be random or default (often 255), since EEPROM memory retains old or default data until written, as implied by the initial 'unknown' state in variable_tracker.

Why do we use Serial.begin before printing?

Serial.begin initializes communication with the computer so Serial.println can send data, which is necessary before printing the value in step 3.

Visual Quiz - 3 Questions

Look at the execution table, what value is read from EEPROM at step 2?

A undefined

B 0

C 42

D 255

💡 Hint

Check the 'Value Read' column at step 2 in the execution_table.

At which step does the program print the EEPROM value?

A Step 1

B Step 3

C Step 2

D Step 4

💡 Hint

Look at the 'Output' column in the execution_table to find when printing happens.

If we change EEPROM.write(0, 100), what will be printed at step 3?

A 100

B 0

C 42

D undefined

💡 Hint

Refer to variable_tracker and execution_table to see how written value affects read and output.

Concept Snapshot

EEPROM.write(address, value) stores a byte persistently.
EEPROM.read(address) retrieves the stored byte.
Always write before reading to get valid data.
Use Serial.begin() before printing.
EEPROM retains data after power off.

Full Transcript

This example shows how Arduino EEPROM memory can store data permanently. First, the program writes the number 42 to EEPROM address 0. Then it reads back the value from the same address. Finally, it prints the value to the serial monitor. The execution table traces each step: writing, reading, and printing. The variable tracker shows how EEPROM[0] changes from unknown to 42, and how the variable val holds the read value. Key moments clarify why writing must happen before reading and why serial communication must start before printing. The quiz tests understanding of these steps and how changing the written value affects output.