What is an EEPROM?
EEPROM stands for electrically erasable programmable read-only memory. It is a non-volatile flash memory device, that is, stored information is retained when the power is removed. EEPROM generally offers excellent capabilities and performance. In EEPROM we can write and program the IC for many times and these are acting as EPROM (UV erasable programming ROM).
However an EEPROM need not be taken out of the computer or electronic device of which it is part when a new program or information or data needs to be written on it. Particular customizing might be finished to an EEPROM chip.
The client/user can change the quality of certain units without expecting to erase the programming on different cells. Consequently, areas of data might be erased and replaced without expecting to adjust whatever rest of the chip programming. Data saved in an EEPROM chip is permanent, until the client chooses to delete and replace the data that it contains. The information saved in an EEPROM chip is not lost even when power is turned off. Here only one external power supply device is used . Write and erase operation are performed on byte basis.
There are many types of EEPROM devices available, but one of the most commonly used EEPROM families is 24CXX series devices such as 24C02, 24C04, 24C08 and etc. These all are have same features but only difference is in its memory.
Features of EEPROM:
- Low and standard voltage operation (100 kHz (1.8V) and 400 kHz (2.7V, 5V) compatibility)
- Schmitt trigger, filtered inputs for noise suppression
- Internally Organized 128 x 8 (1K), 256 x 8 (2K), 512 x 8 (4K), 1024 x 8 (8K) or 2048 x 8 (16K)
- Automotive devices available
- Two-wire serial interface (Two wires are used to read and write data into it)
- Bidirectional data transfer protocol
- Write protect pin for hardware data protection
- 8-byte page (1K, 2K), 16-byte page (4K, 8K, 16K) write modes
- Partial age writes allowed
- Self-timed write cycle
Principle of operation of EEPROM
The EEPROM uses the principle same as that of the UV-EPROM. The electrons which are trapped in a floating gate will modify the characteristics of the cell, so instead of that logic “0” or logic “1” will be stored.
EEPROM is the memory device which implements the fewest standards in cell design. Most of the common cells are composed of two transistors. In this the storage transistor has the floating gate that will trap the electrons. Apart from that there is an access transistor which is used in the operation. In EPROM , cell is erased when electrons are removed from the floating gate, whereas in EEPROM , cell is erased when electrons are trapped in the floating cell.
There are two distinct EEPROM families: serial and parallel access. The serial access represents 90 percent of the overall EEPROM in market, where as the parallel access EEPROMs is about 10 percent.
- Parallel devices are available in higher densities more then 256bits and are generally working faster.
- Highly Reliable and these are mostly used for military market.
- They are pin compatible with EPROMs and flash memory devices.
Parallel EEPROM Devices
- Serial EEPROMs are less dense (typically from 256 bit to 256Kbit) and are slower than parallel devices.
- They are much cheaper and used in more “commodity” applications.
• Operating voltage range Read: 1.8 V to 5.5 V
• Operation frequency: 2.0 MHz (VCC = 4.5 V to 5.5 V)
• Sequential read capable
• Function to protect against write due to erroneous instruction recognition
• Endurance: 106
Cycles / word*1 (Ta = +85°C)
• Data retention: 100 years (Ta = +25°C)
20 years (Ta = +85°C)
• Memory capacity: S-93C46B 1 K-bit
S-93C56B 2 K-bit
S-93C66B 4 K-bit
• Initial shipment data: FFFFh
• Lead-free, Sn 100%, halogen-free*2
Memory Organization of EEPROM
AT24C02 EEPROM: 24C08 are internally organized with 32 pages of 8 bytes each, the 2K requires an 8-bit data word address for random word addressing.
AT24C04 EEPROM: 224C08 are internally organized with 32 pages of 16 bytes each; the 4K requires a 9-bit data word address for random word addressing.
AT24C08 EEPROM: 24C08 are internally organized with 64 pages of 16 bytes each, the 8K requires a 10-bit data word address for random word addressing.
Applications of EEPROM
EEPROMs are used in many applications such as telecom, consumer, automotive and industrial applications. The other applications are include:
1. The reprogrammable calibration data for test equipment
2. Data storage from a learn function as in a remote control transmitter.
The AT24C02 is an electrically erasable programmable read-only memory (EEPROM) chip. It is internally organized with 32 pages of 8 bytes each; it has 2Kbits of memory size. It is most commonly used EEPROM; it comes with 8-pin DIP, shown in figure:
Pin 1-3: A0, A1, A2 are the address inputs of chip, in this A1 and A2 are for addressing and A0 is a NA (no connection) pin. The eight 2K devices may be addressed on a single bus system.
Pin 4: Ground (GND).
Pin 5: It is a serial data pin; it is bi-directional for serial data transfer.
Pin 6: It is serial clock input, provides the positive clock signals.
Pin 7: It is write protect pin, provides the hardware data protection. It allows read/write operation when connected to ground pin.
Pin 8: Power supply.
Application involving EEPROM 24C02
From the circuit, in this we used EEPROM 24C02 of 2KB memory to store the desired password/number entered by the keypad, both of which are interfaced to microcontroller shown in figure. While the user wants to open the lock which is prompted by an LCD display duly connected to the microcontroller, he must enter the password by the keypad. If it is matched with the stored password in the EEPROM retrieved by the microcontroller it delivers logic high at pin38 and 37 to either to open or close the door. For the purpose of the output verification we can use two lamps to indicate door opening and closing.
- EEPROM by Dave Banks
- Parallel EEPROM by encrypted
- Parallel EEPROM Devices by atmel
- Serial EEPROM by encrypted