Information AboutEeprom |
| CATEGORIES ABOUT EEPROM | |
| non-volatile memory | |
| computer memory | |
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OVERVIEW Serial EEPROMs come in a range of capacities from a few bytes to over 128 Kilobyte s and are typically used to store Configuration parameters, and in modern computers they replace the hitherto CMOS Nonvolatile BIOS Memory . For example, in Personal Computer s these chips are used to store the BIOS code and related system settings. Unlike EPROM s, EEPROMs can be programmed and erased electrically. This is the main advantage. EEPROMs are still limited in that repeated write and erase cycles eventually damage the thin insulating layer. Some early EEPROMs could only perform about 100 erase-write cycles. EEPROM should not be confused with RAM (Random Access Memory). While RAM can be re-written many billions of times, EEPROMs can be written only a few hundred to a few thousand times. Also, RAM is generally a lot faster to write than EEPROM (typically a few nanoseconds as opposed to a few microseconds), and most types of RAM are volatile (they lose their contents when power is removed). EEPROM retains its data after powerdown. OPERATION There are different types of electrical interfaces to EEPROM devices. Main categories of these interface types are: How the device is operated depends on the electrical interface. Serial bus devices Most common serial interface types are SPI , I&2C and 1-Wire . The serial EEPROM typically operates in three phases: OP-Code Phase , Address Phase and Data Phase. The OP-Code is usually the first 8-bits input to the serial input pin of the EEPROM device, followed by 16 to 24 bits of addressing depending on the depth of the device. Each EEPROM device typically has its own set of OP-Code instructions to map to different functions. Some of the common operations on SPI EEPROM devices are:
Other operations supported by some EEPROM devices are:
The final phase of operation is typically the data phase. In case of WRITE, the controller needs to supply data until the chip select is low. In case of read, the controller needs to sample the data every serial clock edge until the chip select is low. Parallel bus devices Parallel EEPROM devices typically has an 8-bit data bus and an address bus wide enough to cover the complete memory. Most devices have chip select and write protect pins. Some Microcontrollers also have integrated parallel EEPROM. Operation of a parallel EEPROM is simple and fast when compared to serial EEPROM. RELATED TYPES Flash Memory is a later form of EEPROM. In the industry, there is a convention to reserve the term EEPROM to byte-wise writable memories compared to block-wise writable flash memories. EEPROM takes more die area than flash memory for the same capacity because each cell usually needs both a read, write and erase Transistor where in flash memory the erase circuits are shared by blocks of many (often 512×8) cells. Newer technologies such as FRAM and MRAM are slowly replacing EEPROMs in some applications. Comparison with EPROM EPROM has two significant limitations:
EEPROM can be programmed and erased electrically. The difference between EPROM and EEPROM lies in the thickness of the insulating layer — in an EPROM it is about 3 Nanometres thick whereas in an EEPROM it is much thinner — typically around 1 nanometre. This thinner insulating layer allows for lower voltages to be used for programming. EEPROM MANUFACTURERS SEE ALSO |
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