Memory layout on a microcontroller (Flash, SRAM, EEPROM) in Embedded C - Step-by-Step Execution

Concept Flow - Memory layout on a microcontroller (Flash, SRAM, EEPROM)

Program Start

↓

Load Flash Memory

↓

Initialize SRAM

↓

Access EEPROM

↓

Run Program Loop

↓

End or Reset

This flow shows how a microcontroller uses Flash to store code, SRAM for variables during run, and EEPROM for long-term data.

Execution Sample

Embedded C

const int x = 10;  // stored in Flash
int y = 5;          // stored in SRAM
void main() {
  y = x + 2;
  // EEPROM read/write simulated
}

This code shows constants in Flash, variables in SRAM, and simulates EEPROM usage.

Execution Table

Step	Memory Area	Action	Content	Notes
1	Flash	Store constant x=10	x=10	Flash is non-volatile, stores program code and constants
2	SRAM	Allocate variable y=5	y=5	SRAM is volatile, stores variables during execution
3	SRAM	Execute y = x + 2	y=12	Variable y updated in SRAM
4	EEPROM	Read stored data	data=previous value	EEPROM stores data that persists after power off
5	EEPROM	Write new data	data=updated value	EEPROM write simulated
6	-	Program runs loop or ends	-	Microcontroller continues running or resets

💡 Program ends or resets; SRAM loses data, Flash and EEPROM retain contents

Variable Tracker

Variable	Start (Flash/SRAM/EEPROM)	After Step 2	After Step 3	After Step 5	Final
x (Flash)	10	10	10	10	10
y (SRAM)	undefined	5	12	12	undefined (after reset)
EEPROM data	old value	old value	old value	updated value	updated value

Key Moments - 3 Insights

Why does variable y lose its value after reset but x does not?

Because y is stored in SRAM which is volatile and loses data on power off, while x is stored in Flash which is non-volatile and keeps data.

Can we change the value of x during program execution?

No, x is stored in Flash memory which is read-only during normal operation; only variables in SRAM or EEPROM can be changed.

Why use EEPROM if Flash is also non-volatile?

EEPROM allows data to be changed and saved during program run, unlike Flash which is mainly for code and constants.

Visual Quiz - 3 Questions

Look at the execution table, what is the value of y after Step 3?

A 5

B 12

C 10

D undefined

💡 Hint

Check the 'Content' column for Step 3 in the execution table.

At which step does EEPROM data get updated?

A Step 5

B Step 3

C Step 2

D Step 6

💡 Hint

Look for 'Write new data' action in the execution table.

If the microcontroller resets, which memory area retains its data?

A SRAM only

B EEPROM only

C Flash and EEPROM

D SRAM and Flash

💡 Hint

Refer to the exit note and variable tracker for data retention after reset.

Concept Snapshot

Memory layout on microcontrollers:
- Flash: stores program code and constants, non-volatile
- SRAM: stores variables during execution, volatile
- EEPROM: stores data that must persist across resets
- Variables in SRAM lose data on power off
- Constants in Flash and data in EEPROM persist

Full Transcript

This visual execution shows how a microcontroller uses three main memory areas: Flash, SRAM, and EEPROM. Flash memory holds the program code and constants like x=10. SRAM holds variables like y=5 during program run and changes as the program executes. EEPROM stores data that must be saved even when power is off. The execution table traces storing x in Flash, allocating y in SRAM, updating y, reading and writing EEPROM data, and program running or resetting. Variables in SRAM lose their values after reset, but Flash and EEPROM keep their contents. This helps beginners understand memory roles and data persistence on microcontrollers.