Here's a suggestion. Now i don't know what the operating current for
these devices is BUT how about powering up the flash memory from a PORT
pin. The 16F84 can supply up to 20mA/pin. When not being accessed the
port pin is set LOW, no power is consumed. When the 16F84 is placed into
sleep mode the previous pin states are retained... The only current
being used is the sleep current for the 16F84...

I have used this method for the common garden variety serial eeprom's
with no problems...

Stewart Greenhill wrote:
>
> Hi Folks,
>
> I'm new to the PIC list and am back into PIC development mode after an absence
> of a few years.
>
> I'm working on a data logging application using a PIC16F84. I need a
> low-power design with a large memory. These loggers may be recording for
> several years under battery power before being interrogated.
>
> Currently, I'm looking at a couple of 8 megabit serial flash memory
> devices: the NexFlash NX25F080A and the ATMEL AT45DB081. Both operate at
> 2.7 volts, have a 4-wire serial interface and dual SRAM sector buffers
> on-chip. This is important because it allows sectors to be assembled
> on-chip before being programmed into FLASH. This style of memory requires
> an entire sector to be written at once, and there is not enough RAM in a
> PIC to hold the data.
>
> The ATMEL part looks a little more flexible, since both sector buffers can
> be programmed directly to FLASH. The NexFlash part has separate PROGRAM and
> SRAM buffers; although data can be copied between the two, only the PROGRAM
> buffer can be written to FLASH. However, the decider for me is the power
> consumption. At 2 uA standby, the ATMEL part requires twice the power of
> the NexFlash part (1 uA).
>
> Does anyone have any experience (positive or negative) with either of these
> parts? Are there any other devices that I should consider using?
>
> Thanks,
> - Stewart Greenhill

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