Electrically erasable programmable ROM , or EEPROM, is flash’s predecessor. In fact, some people still refer to flash as “flash EEPROM,” because the underlying structures are very similar. EEPROM, sometimes written as E2PROM, is more expensive to manufacture per bit than EPROM or flash, because individual bytes may be erased randomly without affecting neighboring locations. Because of the complexity and associated cost of making each byte individually erasable, EEPROM is not commonly manufactured in large densities. Instead, it has served as a niche technology for applications that require small quantities of flexible reprogrammable ROM. Common uses for EEPROM are as program memory in small microprocessors with embedded memory and as small nonvolatile memory arrays to hold system configuration information. Serial EEPROM devices can be found in eightpin DIP or SOIC packages and provide up to several kilobytes of memory. Their serial interface, small size, and low power consumption make them very practical as a means to hold serial numbers,
manufacturing information, and configuration data. Parallel EEPROM devices are still available from manufacturers as the 28xx family. They are pin and function compatible (for reads) with the 27xxx EPROM family that they followed. Some applications requiring reprogrammable nonvolatile memory may be more suited to EEPROM than flash, but flash is a compelling choice, because it is the more mainstream technology with the resultant benefit of further cost reduction. Serial EEPROMs, however, are quite popular due to their very small size and low power consumption.
They can be squeezed into almost any corner of a system to provide small quantities of
nonvolatile storage. Microchip Technology is a major manufacturer of serial EEPROMs and offers the 24xx family. Densities range from 16 bytes to several kilobytes. Given that serial interfaces use very few pins, these EEPROMs are manufactured in packages ranging from eight-pin DIPs to fivepin SOT-23s that are smaller than a fingernail. Devices of this sort are designed to minimize system impact rather than for speed. Their power consumption is measured in nanoamps and microamps instead of milliamps, as is the case with standard flash, parallel EEPROM, and EPROM devices.
Microchip’s 24LC00 is a 16-byte serial EEPROM with a two-wire serial bus. It requires only four pins: two for power and two for data communication. Like most modern flash devices, the 24LC00 is rated for one million write cycles. When not being accessed, the 24LC00 consumes about 250 nA! When active, it consumes only 500 μA. For added flexibility, the 24LC00 can operate over a variety of supply voltages from 2.5 to 6.0 V. Speed is not a concern here: writes take up to 4 ms to complete, which is not a problem when writing only a few bytes on rare occasions.
manufacturing information, and configuration data. Parallel EEPROM devices are still available from manufacturers as the 28xx family. They are pin and function compatible (for reads) with the 27xxx EPROM family that they followed. Some applications requiring reprogrammable nonvolatile memory may be more suited to EEPROM than flash, but flash is a compelling choice, because it is the more mainstream technology with the resultant benefit of further cost reduction. Serial EEPROMs, however, are quite popular due to their very small size and low power consumption.
They can be squeezed into almost any corner of a system to provide small quantities of
nonvolatile storage. Microchip Technology is a major manufacturer of serial EEPROMs and offers the 24xx family. Densities range from 16 bytes to several kilobytes. Given that serial interfaces use very few pins, these EEPROMs are manufactured in packages ranging from eight-pin DIPs to fivepin SOT-23s that are smaller than a fingernail. Devices of this sort are designed to minimize system impact rather than for speed. Their power consumption is measured in nanoamps and microamps instead of milliamps, as is the case with standard flash, parallel EEPROM, and EPROM devices.
Microchip’s 24LC00 is a 16-byte serial EEPROM with a two-wire serial bus. It requires only four pins: two for power and two for data communication. Like most modern flash devices, the 24LC00 is rated for one million write cycles. When not being accessed, the 24LC00 consumes about 250 nA! When active, it consumes only 500 μA. For added flexibility, the 24LC00 can operate over a variety of supply voltages from 2.5 to 6.0 V. Speed is not a concern here: writes take up to 4 ms to complete, which is not a problem when writing only a few bytes on rare occasions.
