module 4

Memory

Memory in Embedded Systems

1. Read-Only Memory (ROM)

2. Random Access Memory (RAM)

3. Memory According to the Type of Interface

4. Memory Shadowing

5. Memory Selection for Embedded Systems

ROM

Read-Only Memory

Read-Only Memory (ROM)

• a non-volatile type of memory commonly used in embedded systems.

• data stored in ROM cannot be modified or erased once it is programmed during manufacturing.

• is a type of memory that retains its contents even when the power is turned off

• used to store firmware, boot loaders, and system configuration data that are essential for the functioning of an embedded system

• is often referred to as "non-volatile" because it retains data without the need for a continuous power supply.

• The data stored in ___ is non-erasable and non-modifiable, making it ideal for storing critical system information

Types of ROM

1. Mask ROM

2. PROM (Programmable Read-Only Memory)

3. EPROM (Erasable Programmable Read-Only Memory)

4. EEPROM (Electrically Erasable Programmable Read-Only Memory)

5. Flash Memory

Mask ROM

This type of ROM is manufactured with a fixed pattern during the chip fabrication process. The data is permanently embedded in the ROM, and it cannot be changed or updated

PROM (Programmable ROM)

allows users to program the memory once by using special programming equipment. Once programmed, the data becomes permanent and cannot be altered

EPROM (Erasable Programmable ROM)

is similar to PROM but can be erased and reprogrammed using ultraviolet light exposure. It requires a special erasing device to remove the existing data before reprogramming.

EEPROM (Electrically Erasable Programmable ROM)

can be electrically erased and reprogrammed using specific voltage levels. Unlike EPROM, it does not require UV light for erasing and is more convenient for in circuit updates.

Flash Memory

is a type of EEPROM that allows multiple-byte erasure. Widely used in embedded systems due to its high density, fast erasure, and reprogramming capabilities

Most embedded systems, such as microcontrollers (e.g., Arduino), use _____________ to store sketches.

retains its contents without power and can be electrically erased and reprogrammed.

Applications of ROM

• Firmware Storage

• Boot Loaders

• System Configuration Data

Limitations

• it cannot be modified or updated once programmed

• higher manufacturing costs

• require upfront design decisions

RAM

Random Access Memory

Random Access Memory (RAM) Definition and Characteristics

• Volatile memory

• Allows read and write operations

• Examples: Static RAM (SRAM), Dynamic RAM (DRAM)

Random Access Memory (RAM) Applications and Limitations

• Storing program code, data, and variables during runtime

• Faster access but larger in size compared to ROM

Random Access Memory (RAM)

is a type of volatile memory commonly used in embedded systems. It is called "random access" because it allows for both read and write operations, and data can be accessed in any order, unlike sequential access memory.

Static RAM (SRAM)

Fast, more expensive, used for small, high-speed applications.

Dynamic RAM (DRAM)

Slower, cheaper, used for larger memory needs.

Parallel Memory Interfaces

_______________ allow multiple bits of data to be transmitted simultaneously. This type of memory is typically faster due to the simultaneous transfer of data bits.

Serial Memory Interfaces

_____________________ transmit data one bit at a time, which can lead to lower complexity and reduced pin count.

Memory-Mapped Interfaces

In embedded systems, certain memory types can be accessed as part of the system's address space

a method of interfacing hardware devices with a microcontroller through memory addresses.

Specific memory addresses in the system’s address space are allocated for hardware devices, allowing them to be accessed like regular memory locations. Hardware devices (like sensors) are assigned specific addresses within the main memory range.

This means that the CPU can read from or write to these devices using standard memory operations.

Direct Memory Access (DMA)

_______ allows peripherals to access memory without CPU intervention, optimizing data transfer rates:

Characteristics: Reduces CPU load and improves system performance. Commonly used in applications requiring high-speed data transfer, like audio and video processing.

Memory-Mapped I/O

Memory Shadowing

is a technique used to improve performance and reliability by creating a duplicate or "shadow" copy of a section of memory.

- Duplicating critical data or program code in a secondary memory space.

- Purpose is to ensure that the system can continue to operate correctly even in the event of a fault or error in the primary memory.

Key Characteristics of Memory Shadowing

• Redundancy

• Performance Improvement

• Error Detection and Recovery

Common Factors for Selecting Memory in Embedded Systems

1. Type of Memory

2. Performance Requirements

3. Capacity Needs

4. Power Consumption

5. Cost

6. Reliability and Durability

7. Interface Compatibility

8. Data Retention

9. Size and Form Factor

10. Availability and Support

Comparison of ESP32 and Arduino Uno