Electrically Erasable Programmable Read-Only Memory is a non-volatile memory technology, that allows electronic data to be erased & reprogrammed multiple times. It is widely used in various electronic devices, including microcontrollers, computers, and consumer electronics. There are several types of EEPROM, each with its unique characteristics and applications.
What is EEPROM?
EEPROM is an Electrically Erasable Programmable Read Only Memory, that is erased, reprogrammed, or written repeatedly using electrical signals. Moreover, it is a type of non-volatile and modified version of EPROM.
Basically, Electrically Erasable Programmable Read Only Memory enables individual bytes of data that can be erased and rewritten. Hence, EEPROM chips are termed byte erasable chips. It is usually used to store a small amount of data in computing and other electronic devices. EEPROM devices may sometimes fail due to data sufferance and data existence time. One of the commonly used EEPROM chips is the 24CXX series that contains several models.
History
Researchers at Hughes Aircraft and Intel, developed EEPROM in the year 1978. It was used as replacement of EPROM and PROM. EPROM technology was used widely before the use of Electrically Erasable Programmable Read Only Memory. The biggest disadvantage of EPROM was if in case it is exposed to ultraviolet rays, the whole programmed memory could be accidently erased. EEPROM overcame this issue and it can only be programmed or erased using specific Electrical Signals. EEPROM chips have a life span of 10,000 to 1,00,000 write cycles, comparatively more than EPROM chips.
Types of Electrically Erasable Programmable Read Only Memory
There are two types of EEPROM memory chips available –
Serial EEPROM
Serial EEPROMs utilize a serial interface for data communication. These EEPROMs are widely used due to their small package size, low power consumption, and ease of integration with microcontrollers. Serial EEPROMs are commonly employed in applications that require small amounts of non-volatile memory. These chips contain small eight-pin package and are less expensive. The data is transferred serially and slowly.
Types of Serial EEPROM
Below mentioned are some of the standard interface types that are available:–
- Serial Peripheral Interface
- Inter-Integrated circuit
- Microwire
- UNI/O
- 1-Wire
Serial Peripheral Interface
SPI EEPROMs utilize the Serial Peripheral Interface (SPI) for communication. SPI is a synchronous serial communication protocol widely supported by microcontrollers and other integrated circuits. They offer high-speed data transfer and are commonly used in applications that require faster read and write operations.
Inter-Integrated Circuit (I2C) EEPROM
I2C EEPROMs are a specific type of serial EEPROM that follows the I2C communication protocol. I2C is a widely used serial communication standard that allows multiple devices to be connected on a common bus. They are popular in applications where simplicity, low pin count, and ease of integration are essential.
Microwire EEPROM
Microwire EEPROMs are another type of serial EEPROM that employs the Microwire interface. The Microwire protocol is a synchronous, three-wire interface commonly used in automotive and industrial applications. Microwire EEPROMs offer a balance between simplicity, low pin count, and moderate data transfer rates.
UNI/O EEPROM
UNI/O EEPROM is a specific type of serial EEPROM that utilizes a simplified and space-saving communication protocol called UNI/O. With a small package size and low pin count, UNI/O EEPROMs are ideal for compact devices where simplicity and efficient space utilization are crucial. These EEPROMs employ a single bidirectional data line for communication, simplifying wiring and reducing system complexity.
UNI/O EEPROMs are available in various memory capacities, catering to different application requirements in consumer electronics, automotive systems, and industrial control applications. The UNI/O protocol requires adherence to specific command structures and timing sequences, ensuring accurate communication between the microcontroller and the EEPROM.
1-Wire EEPROM
1-Wire EEPROM is a specific type of serial EEPROM that uses a unique communication protocol known as the 1-Wire interface. The 1-Wire interface enables data transfer and power delivery over a single data line, simplifying wiring and reducing pin count in applications. They are commonly used in systems requiring low pin count, low power consumption, and simplicity, such as temperature sensors, identification devices, and small embedded systems.
These EEPROMs are designed to operate with a single data line and do not require external components like additional control lines or clocks. 1-Wire EEPROMs come in various memory capacities and are known for their reliability, ease of integration, and compatibility with a wide range of microcontrollers and devices.
EEPROM Serial Protocol
The EEPROM serial protocol are inclusive of following three phases:-
- Operation code phase
- Address phase
- Data phase
Operation Code Phase
In this phase, the microcontroller or host device sends an operation code to the EEPROM, indicating the desired operation to be performed. The operation code specifies whether the intention is to read data, write data, erase data, or perform other operations supported by the Electrically Erasable Programmable Read Only Memory.
Address Phase
Following the operation code phase, the microcontroller sends the memory address to the EEPROM. The address identifies the specific location in the EEPROM where the read or write operation should be performed. The address phase is crucial for accessing the desired memory location accurately.
Data Phase
Once the EEPROM receives the operation code and address, it enters the data phase. During this phase, data is either read from the EEPROM and sent back to the microcontroller or new data is written into the specified memory location. The data phase involves the actual transfer of data between the microcontroller and the EEPROM, enabling the desired read or write operation.
Parallel EEPROM
Unlike serial EEPROMs, parallel EEPROMs use a parallel interface for data transfer. They offer faster read and write speeds compared to serial EEPROMs. However, parallel EEPROMs often require more pins and additional control signals, making them less suitable for space-constrained applications. These EEPROMs are commonly found in legacy systems and applications that require higher data throughput.
Characteristics
Electrically Erasable Programmable Read-Only Memory possesses distinctive characteristics that contribute to its widespread utilization in various applications. Below are the key characteristics:
Non-Volatile Memory
EEPROM is classified as a non-volatile memory technology, ensuring that stored data remains intact even when power is removed. This quality makes it highly suitable for applications requiring persistent data storage.
Electrically Erasable
Unlike earlier forms of memory such as EPROM, EEPROM allows for the individual erasure and reprogramming of memory cells through electrical means. This eliminates the need for UV light exposure during the erasure process, resulting in a more convenient and efficient memory manipulation process.
Random Access
EEPROM facilitates random access to memory cells, permitting direct reading from or writing to any specific memory location. This capability enables flexible data manipulation and efficient management of stored information.
Byte-Level Read and Write
Electrically Erasable Programmable Read Only Memory supports the reading and writing of data at the granularity of individual bytes. This fine-grained control enables precise modification or updating of specific segments of data stored within the EEPROM.
Limited Endurance
Each memory cell within an EEPROM has a limited endurance, indicating the maximum number of erase/write cycles it can endure reliably. The endurance level is typically provided by the manufacturer and should be considered when designing systems that involve frequent data modifications.
Small Form Factor
EEPROMs are available in compact package sizes, making them highly suitable for applications with space constraints where size optimization is crucial. This characteristic allows for easy integration of EEPROM into various electronic devices and systems.
Low Power Consumption
EEPROMs typically exhibit low power requirements, enabling efficient operation within power-constrained devices. This attribute is particularly valuable in applications powered by batteries or devices that prioritize energy efficiency.
Advantages
- EEPROM can be reprogrammed multiple times.
- The contents can be erased byte-by-byte as the data stored is non-volatile.
- The data can be erased electrically.
- Chips need not be removed from the system while modifying unlike EPROM.
- No need of extra equipment to change the content.
Disadvantages
- EEPROM needs varieties of voltages for reading, writing and erasing the content.
- It is more expensive when compared to PROM and EPROM.
- It has limited data retention time.
- For the systems that use EEPROM chips they might issues with pricing.
- The read or write cycles are comparatively slower when compared to the cycles on RAM. Hence, in order not to slow down, it is very important to use the data stored in EEPROM.
- The serial EEPROM requires more time to execute the program.
Brief About EEPROM Transistors
Electrically Erasable Programmable Read-Only Memory transistors are the key components used in EEPROM memory cells to store and manipulate data. In EEPROM, the process of erasing the charge is typically performed using a metal-oxide-semiconductor (MOS) transistor.
Courtesy: PCMag
The utilization of MOS transistors, particularly floating gate transistors, in EEPROM allows for the storage and manipulation of charge to represent data. The erasing process involves removing the charge from the floating gate, thereby resetting the logic state of the memory cell.
The primary purpose of the floating gate transistors (FGTs) in EEPROM is to hold the charge. The fundamental building block of an EEPROM memory cell is a floating gate transistor. It consists of a control gate, a floating gate, a source, and a drain. The floating gate is insulated, typically by a thin oxide layer, and is electrically isolated from the other components.
Principle of Operation
The principle of operation of EEPROM (Electrically Erasable Programmable Read-Only Memory) involves the use of electric signals to store, erase, and read data in non-volatile memory cells.
Memory Cell Structure
EEPROM consists of a grid of memory cells, organized into rows and columns. Each memory cell is made up of a floating gate transistor, which contains a floating gate and a control gate. The floating gate is insulated, preventing the charge stored on it from dissipating.
Data Storage
The state of a memory cell in EEPROM is determined by the presence or absence of electrical charge on the floating gate. To program a memory cell, a high voltage is applied to the control gate, allowing electrons to tunnel through the insulating layer onto the floating gate. This trapped charge on the floating gate alters the transistor’s threshold voltage, determining whether the cell is in a programmed (charged) or erased (uncharged) state, representing binary data (0 or 1).
Data Readout
To read data from an EEPROM cell, a moderate voltage is applied to the control gate. The transistor’s conduction is determined by the threshold voltage, which is influenced by the charge on the floating gate. By sensing the transistor’s conduction, the stored data (0 or 1) can be read.
Data Erasure
Unlike traditional EEPROM, which required exposure to ultraviolet light for erasure, electrically erasable EEPROM allows for erasure at the cell level. To erase a cell, a higher voltage is applied to the control gate, creating a strong electric field that facilitates the removal of charge from the floating gate, returning the cell to an erased state.
Addressing and Control
EEPROM memory cells are organized into a matrix. Each cell is identified by a unique address, allowing for random access to individual cells for programming, reading, or erasing. Control circuitry manages the operations, including addressing, data transfer, and voltage application, ensuring accurate and reliable operations.
Memory Organization
EEPROM memory is organized into individual memory cells, each capable of storing a certain amount of data. The memory cells are typically arranged in a matrix or array structure.
The most common organization in Electrically Erasable Programmable Read Only Memory is the byte organization. In this organization, the memory is divided into individual bytes, with each byte having its unique address. Bytes are typically grouped into pages, where a page consists of several consecutive bytes. The size of a page can vary depending on the specific EEPROM device.
The byte organization allows for random access to individual bytes, enabling flexibility in reading and writing data. It is also possible to erase or modify individual bytes without affecting the rest of the memory.
In addition to the byte organization, some EEPROM devices also support other memory organization schemes, such as word organization or sector organization. Word organization groups multiple bytes together as a single word, typically 2 or 4 bytes in size. Sector organization divides the memory into larger sectors, which may contain multiple pages or blocks of memory.
The choice of memory organization depends on the specific requirements of the application. Byte organization is often favored for its flexibility and ease of use, especially when dealing with small-scale data storage and frequent random access. Word or sector organization may be preferred for applications that involve larger chunks of data or require more efficient memory management.
It is important to consult the manufacturer’s documentation or datasheet of a specific EEPROM device to understand its memory organization, including the size of pages, sectors, or other relevant units, as it can vary between different EEPROM models.
How EEPROM is Programmed and Erased?
Electrically Erasable Programmable Read-Only Memory can be programmed and erased using specific electrical signals and operations.
Programming EEPROM
Courtesy: Wikipedia
- To program an EEPROM cell, a higher voltage is applied to the control gate, which is typically referred to as the programming voltage.
- The programming voltage enables electrons to tunnel through the insulating layer onto the floating gate of the memory cell.
- The trapped charge on the floating gate alters the transistor’s threshold voltage, determining whether the cell is in a programmed state (charged), representing a logic 1.
- The specific programming mechanism and voltage requirements may vary depending on the EEPROM device’s architecture and technology.
Erasing EEPROM:
Courtesy: Wikipedia
- EEPROM erasure is typically done at the block or sector level rather than at the individual cell level.
- There are two common methods for erasing EEPROM: electrical erasure and global erasure.
- Electrical erasure: In this method, a higher voltage, often referred to as the erase voltage, is applied to the control gate. The high voltage creates an electric field that removes the charge from the floating gate, returning the cell to an erased state (uncharged), representing a logic 0.
- Global erasure: Some EEPROM devices support a global erasure method where all memory cells are simultaneously erased. We can achieve this by applying a specific sequence of voltage pulses or by using internal circuitry designed for global erasure.
Applications
Usage of EEPROM in various sectors like:-
- In telecom sector, consumer, automotive and industrial applications.
- The reprogrammable comparison of data for test equipment.
- Storage of data from a learn function as in a remote-control transmitter.
Author’s View
Electrically Erasable Programmable Read Only Memory is advanced level data storage. Moreover, it is a type of flash memory and hence it is fast and has the advantage of accessing and changing any code byte-wise. While a user is rewriting or deleting the data, EEPROM accesses the data byte-wise. It is widely used in the computer systems and microcontrollers where a small amount of data is stored. Additionally, it is also used in certain cases where the code is changed. However, when compared to other devices, they are quite expensive.
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