Comparison Between DataFlash, EEPROM and MMC/SD
Both DataFlash and EEPROM chips can be accessed from a microcontroller, using a 4-wire SPI bus. Both are available in small 8 pin packages. The protocol interfaces are very similar; in both cases, bytes are written or read, via SPI, one or more bytes at a time.
DataFlash usually had higher capacities than EEPROM in the early days, and it still provides faster access times. DataFlash capacities in small packages range from 128 kB to 8 MB, while SPI EEPROM capacities in similar packages range from 1 kB to 8 MB . Flash chips are tuned for page access, rather than the byte access used with EEPROM. However, AT45 series chips have commands that let their drivers act more like EEPROM drivers. Leveraging the SRAM buffers exposed by AT45 chips to do more than support EEPROM-like access requires specialized software.
DataFlash cards are more expensive than the consumer oriented MMC or SD cards, and have lower capacities, but have an extremely simple programming interface compared to MMC/SD. All these cards can be used in SPI mode.
In summary, DataFlash enables use of more data storage and faster access times than EEPROM. DataFlash chips can leverage the AT45 SRAM buffers. EEPROMs, AT26 series chips, or MMC/SD cards permit use of second sources for parts.
For cards used in field upgrades, DataFlash cards permit simple software support and compatibility with on-board flash chips; MMC/SD costs less.
The programming code required to interface EEPROM to the DataFlash chip is simpler.
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