How to Refresh SRAM? Power Lost & Data Erased

Discussion in 'Embedded Systems and Microcontrollers' started by SaMirakle, Jul 13, 2012.

  1. SaMirakle

    Thread Starter New Member

    Mar 6, 2012
    Hello everyone,

    I have a board with 2 SRAM chips on it. The board has a standby battery to maintain the volatility on the SRAMs. However, the battery died and I'm pretty positive the data on the SRAMs has been erased.

    How can I possibly refresh the data back onto the SRAMs? I have ordered 2 "brand new" SRAMs of the same part but I don't know how to go about programming them. I can't possibly just install the new ones onto the board because theoretically they'd be blank and need to be refreshed as well since they haven't been connected to any power source.

    Would I have to install them onto the board and write to them on-board while they're powered or can I just install them the way they are?

    Thanks so much in advance!
  2. BMorse

    AAC Fanatic!

    Sep 26, 2009
    usually SRAM's are used by a controller to hold volatile data...... so, the board they are on would most likely be able to "reprogram" the data back into the original SRAM's..... unless the board designers used the SRAM's as the main program holder then, you most likely will have to figure out how they programmed the board to begin with...
  3. Papabravo


    Feb 24, 2006
    The concept of being erased does not exist for SRAM (aka Static Random Access Memory). What happened when the battery died was that the data was lost. When the power is reapplied to an SRAM chip all the cells come up in a random, unknown, and uninitialized state.

    The battery does not "maintain the volatility," it prevents the SRAM from being volatile. IMHO there is absolutely no possibility of recovering the data that was in the SRAM. Sorry Charlie!
  4. GetDeviceInfo

    AAC Fanatic!

    Jun 7, 2009
    and as such, data held in sram is temporary in nature. I'd query your need to recover such data.
  5. absf

    Senior Member

    Dec 29, 2010
    I have a Canon Organizer which run on 3 button cells. 2 for the processor and one for the SRAM backup. At the back of the organizer, there is a sticker for the procedure on how to change the batteries.

    When all the batteries are weak, always change the 2 processor batteries before changing the memories backup battery. The memories backup battery should be changed once every year to prevent loss of data.

    In some Yamaha electone keyboards, the song data and music registrations are also stored in SRAM backup by battery. Nowadays they are almost all replaced by flash memories.

    Last edited: Jul 13, 2012
  6. osx-addict


    Feb 9, 2012
    My understanding of SRAM is that it does not consume much power and you can change the battery without losing the content IF you're fairly quick about it and depending on the hardware design.. If you remember the old Palm-Pilot hand-held devices from the 90's, they ran off a pair (IIRC) of AA batteries and would hold the charge for minutes before it would disappear. Anyway, SRAM is, as mentioned above, temporary and not anything like ROM or FLASH.. Once it's been cleared there is NO way to recover whatever was in it -- the data will need to be re-built from scratch by whatever the microcontroller writes into it..
  7. nsaspook

    AAC Fanatic!

    Aug 27, 2009
    Those devices had a capacitor or aux battery backup circuit to maintain the SRAM voltage for a time to allow for "quick" battery changes. Without the backup circuit the data loss would be instantaneous as the data is stored by the logic state of active devices inside the chips.
    My old HP-95XL (it still works) uses a silver-oxide cell for SRAM backup.

    Backup caps:
  8. SaMirakle

    Thread Starter New Member

    Mar 6, 2012
    Hmm... Thanks for all of the input guys.

    Okay, so here's another question then: What if I had a similar boards where the SRAM's were still functioning and data hasn't been lost on them. Could I possibly read the data from them and write them to the SRAMs which lost power (while they're on the board being powered up)?

  9. GetDeviceInfo

    AAC Fanatic!

    Jun 7, 2009
    I opened up an older HMI today that had a battery backed SRAM which held the Win XPe operating system. Needless to say it's been lost.

    A quick look at the bios shows various boot options and the board has IDE ports.

    So here's my plan. Boot into win pe on hard drive, tap the system, compile an xpe image, first boot off harddrive, prep the sram module, copy all files to the module. No gaurantee that will work, but it's a plan.

    First I'll be googling the manufacturer of the device to see if they have an image to download and transfer utility.

    Tell us more about your system.
  10. circuitcruiser

    New Member

    Oct 25, 2012
    Did you ever find a way? I also have boards that has the program stored in flash but need to extract it in order to repair other boards. Any help would be much appreciated. I'm also willing to pay for someone to do this for me if need be.