[sdiy] SRAM question

[Eric Brombaugh]

On 02/19/2010 10:25 AM, Ian Smith wrote:
>
> I have a question about SRAM chips and batteries for memory.
>
> How exactly does this work? using a battery to retain the data saved in the chip?

Typically you'll find either an MCU with internal RAM, or external RAM 
chip driven by a small lithium coin cell. There's an arrangement of 
diodes, either discrete or internal to the chips, which allows either 
the battery, or the power supply to provide sufficient bias to keep the 
RAM from losing its data without overcharging or draining the battery.

Sometimes there is additional protection circuitry to prevent the 
processor from accidentally writing to RAM during power up/down when it 
might do unpredictable things.

While this was pretty common 10-20 years ago, these days more often 
you'll find long-term storage is done with flash memory or EEPROM which 
needs no battery to retain its data.

Eric