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Using NVRAM in embedded projects

NVRAM(Non-Volatile Random Access Memory) is one of the non-volatile memory selections. This may be an alternative to EEPROM to back up the memory. NVRAM chips can be used for nonvolatile memory storage with many benefits comparing to EEPROM. The main benefit is that NVRAM chips work like static RAM. They are RAM; they contain a lithium cell battery for retaining RAM contents when the main power is switched off. The backup memory can store contents as long as the battery provides power. NVRAM chips don’t require much power; backup can be guaranteed for up to ten years.

Dallas NVRAM chip DS1225

For instance lets take Dallas NVRAM chip DS1225.

It contains 64k(8k x 8) of RAM. Chip has an internal battery built-in, so you don’t have to take care of additional backup power. Memory can hold contents for about 10 years without relying only on the internal battery. Using NVRAM gives unlimited write cycles, while EEPROM is limited to like 100000 times. Also, content is protected during sudden external power loss. The main benefits I can see are operation speed and unlimited write cycles. IF application needs constantly update backup memory contents, EEPROM 100000 write cycle limit may exceed very fast. In this case, it is better to use NVRAM—same situation with speed. EEPROM is quite slow memory, and sometimes there would not be enough performance to store incoming backup data. NVRAM speed is the same as SRAM, so there can be stored data and the application itself.

DS1225 NVRAM also matches pin-out with 2764 and 2864 EEPROM. Chip. So it is easy to substitute chips if needed.

Truly speaking, NVRAM memory isn’t that popular as there are more nonvolatile alternatives like FLASH memory, which is providing really high performance for a low price. But NVRAM with static RAM inside still provides significant speed comparing to FLASH.

Last word about confusing. Like many manufacturers like to write, Dallas Semiconductors like to describe memory size in bits like on DS1225, they write 64K, but actually, it is an 8-kilobyte memory chip. Don’t get tricked.

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