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'[EE]: How to retain data in memory when power is o'
2001\12\26@203844 by Randy Poon

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Hello,

My microcontroller circuit generates some important data when running, the data
is now stored in RAM, but I want to retain it even when the power is off. Is
there any way to do this other than using backup battery?

Cheers!

Randy




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2001\12\26@210419 by David VanHorn

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At 05:27 PM 12/26/01 -0800, Randy Poon wrote:
>Hello,
>
>My microcontroller circuit generates some important data when running, the
>data
>is now stored in RAM, but I want to retain it even when the power is off. Is
>there any way to do this other than using backup battery?

External FRAM or EEPROM works.

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2001\12\26@221344 by Aaron Blohowiak

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Whats the difference between the two (or is it only name?)

Thanks
Aaron

Prev. Msg:
[snip]
External FRAM or EEPROM works.
[/snip]

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2001\12\27@062127 by dr. Imre Bartfai

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Hi,

if the amount of data is not huge AND you use appropriate PIC (16F87x,
16CE6xx or 16F84), you can use the internal EEPROM. Advantage: no external
part required, simple programming (except 16CE6xx).
I hope this helps.
Imre


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On Wed, 26 Dec 2001, Aaron Blohowiak wrote:

{Quote hidden}

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2001\12\27@072559 by Bala Chandar

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Imre Bartfai wrote:

> if the amount of data is not huge AND you use appropriate
> PIC (16F87x, 16CE6xx or 16F84), you can use the internal EEPROM.
> Advantage: no external part required, simple programming (except
> 16CE6xx).
> I hope this helps.

Hi Imre,

Your suggestion is very effective, practical and easy to implement without
any additional hardware. Secondly, since there is no battery, there is no
hassle of having to remember to replace the battery once in a year or so.
One requirement of course is that the PIC used should have internal EEPROM.

I use only flash devices (16F628, F870 & F877) and I have used precisely the
same technique in my remote control project that uses 8 relays for
controlling lights and fans. The status of the relays is stored in a byte
and this byte gets saved in the EEPROM every time a relay is turned on or
off. On power-up, this byte value from the EEPROM is read into a variable
that controls the relays.

Assuming the life of each location in the EEPROM is one million erase-write
cycles, if the status of the relay changes 100 times per day, then the
device will last for more than 27 years! Even assuming I continue to use the
gadget, I can switch to another location in the EEPROM for another 27
years!!

I would like to know what others have to say on the subject.

Regards,

Bala

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2001\12\27@095012 by uter van ooijen & floortje hanneman

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> I would like to know what others have to say on the subject.

Not from first hand, but I have often heard of problems with the internal
eeprom (on 16x84's) when no brown-out protection was used. The newer flash
pics have build-in brown-out detection, but I don't know whether this
provides adequate protection against random overwrites.

Wouter van Ooijen

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2001\12\27@104907 by Paul Hutchinson

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>I use only flash devices (16F628, F870 & F877) and I have used precisely
<snip>
>variable that controls the relays.
>
>Assuming the life of each location in the EEPROM is one million
>erase-write cycles, if the status of the relay changes 100 times per
>day, then the device will last for more than 27 years! Even assuming I
>continue to use the gadget, I can switch to another location in the
>EEPROM for another 27 years!!

The 16F87X data-sheet shows the life of the EEPROM as 100,000, not 1
million, at 5V and 25degC. So, on that series of chips the life would be
less than 3 years and, if the temperature gets hotter than 25C the life will
be shorter.

Paul

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2001\12\27@112927 by Randy Poon

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> if the amount of data is not huge AND you use appropriate PIC (16F87x,
> 16CE6xx or 16F84), you can use the internal EEPROM. Advantage: no external
> part required, simple programming (except 16CE6xx).

What if the amount of data is about 64K Bytes?

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2001\12\27@115356 by Harold M Hallikainen

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On Wed, 26 Dec 2001 21:04:33 -0500 David VanHorn <spamBeGonedvanhornspamBeGonespamCEDAR.NET>
writes:
> At 05:27 PM 12/26/01 -0800, Randy Poon wrote:
> >Hello,
> >
> >My microcontroller circuit generates some important data when
> running, the
> >data
> >is now stored in RAM, but I want to retain it even when the power
> is off. Is
> >there any way to do this other than using backup battery?
>
> External FRAM or EEPROM works.
>

       Or, use a PIC that internal EEPROM...

"The ideal design has zero parts."

Harold


FCC Rules Online at http://hallikainen.com/FccRules
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2001\12\27@134018 by Jeff DeMaagd

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At 08:27 AM 12/27/01 -0800, you wrote:
> > if the amount of data is not huge AND you use appropriate PIC (16F87x,
> > 16CE6xx or 16F84), you can use the internal EEPROM. Advantage: no external
> > part required, simple programming (except 16CE6xx).
>
>What if the amount of data is about 64K Bytes?

It would have been more helpful if you had been as specific as possible
with your requirements, and had all your known requirements in the first
mail, as you can see, the lack of information given resulted in a lot of
suggestions that aren't helpful because we don't know what you are looking for.

Jeff

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2001\12\27@141314 by Barry Gershenfeld

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Ferroelectric RAM is a different technology than "Flash".  And there
are at least two kinds of Flash.   The end result is the
same though--nonvolatile memory.

You can learn about FRAM at http://www.ramtron.com

Barry

At 10:02 PM 12/26/01 -0500, you wrote:
{Quote hidden}

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2001\12\27@151626 by Byron A Jeff

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On Thu, Dec 27, 2001 at 11:03:30AM -0800, Barry Gershenfeld wrote:
> Ferroelectric RAM is a different technology than "Flash".  And there
> are at least two kinds of Flash.   The end result is the
> same though--nonvolatile memory.

There are some fundamental differences:

1) Ferro has read and write speeds in the nanosecond range.
2) Ferro is destructive on both reads and writes unlike Flash. So you can wear
Ferro out by reading it too many times. However endurances are topping the
one trillion read/write range on some parts.

So which part you use depends on how you are going to use it.

BAJ

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2001\12\27@161208 by Bob Barr

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On Thu, 27 Dec 2001 15:13:59 -0500, Byron A Jeff wrote:
<snip>

>2) Ferro is destructive on both reads and writes unlike Flash. So you can wear
>Ferro out by reading it too many times. However endurances are topping the
>one trillion read/write range on some parts.
>

Ramtrom rates most of their serial parts at 10^10 (10 billion)
read/writes. (I would presume that their byte-wide memories have the
same limitation but I don't have a datasheet handy to confirm this.)

They claim "unlimited read/writes" for their FM24CL16, a 2 Kbyte
serial device that runs on 2.7 to 3.6 volts Vdd.
They would appear to be migrating to 3-volt SOIC-only (no DIP listed)
parts to replace their older parts and remove the endurance limits.

Regards, Bob

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2001\12\27@164420 by Aaron Blohowiak

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i did some reading.. they offer a 256Kb ( 32 kilobytes) unlimited read/write

"The 256Kb 2.7-3.6 volt FM18L08 offers virtually unlimited read/write
cycles. You can now access each address a million times per second for
hundreds of years with no wear out. "

Aaron

[&quote]
Ramtrom rates most of their serial parts at 10^10 (10 billion)
read/writes. (I would presume that their byte-wide memories have the
same limitation but I don't have a datasheet handy to confirm this.)

They claim "unlimited read/writes" for their FM24CL16, a 2 Kbyte
serial device that runs on 2.7 to 3.6 volts Vdd.
[/&quot]

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2001\12\27@164832 by David VanHorn

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At 04:43 PM 12/27/01 -0500, Aaron Blohowiak wrote:
>i did some reading.. they offer a 256Kb ( 32 kilobytes) unlimited read/write
>
>"The 256Kb 2.7-3.6 volt FM18L08 offers virtually unlimited read/write
>cycles. You can now access each address a million times per second for
>hundreds of years with no wear out. "

Sounds like unlimited to me.

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2001\12\27@180404 by Bob Barr

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On Thu, 27 Dec 2001 16:49:15 -0500, David VanHorn wrote:

>At 04:43 PM 12/27/01 -0500, Aaron Blohowiak wrote:
>>i did some reading.. they offer a 256Kb ( 32 kilobytes) unlimited read/write
>>
>>"The 256Kb 2.7-3.6 volt FM18L08 offers virtually unlimited read/write
>>cycles. You can now access each address a million times per second for
>>hundreds of years with no wear out. "
>
>Sounds like unlimited to me.

That should be close enough. :=)

Regards, Bob

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2001\12\27@195805 by Randy Poon

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Is FRAM available only from Ramtrom? Where can I buy a small quantity of FRAM?

>
> >2) Ferro is destructive on both reads and writes unlike Flash. So you can
> wear
> >Ferro out by reading it too many times. However endurances are topping the
> >one trillion read/write range on some parts.
> >
>
> Ramtrom rates most of their serial parts at 10^10 (10 billion)
> read/writes. (I would presume that their byte-wide memories have the
> same limitation but I don't have a datasheet handy to confirm this.)
>
> They claim "unlimited read/writes" for their FM24CL16, a 2 Kbyte
> serial device that runs on 2.7 to 3.6 volts Vdd.
>
> They would appear to be migrating to 3-volt SOIC-only (no DIP listed)


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2001\12\28@034421 by Roman Black

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wouter van ooijen & floortje hanneman wrote:
>
> > I would like to know what others have to say on the subject.
>
> Not from first hand, but I have often heard of problems with the internal
> eeprom (on 16x84's) when no brown-out protection was used. The newer flash
> pics have build-in brown-out detection, but I don't know whether this
> provides adequate protection against random overwrites.


One solution is to use multiple eeprom bytes for
each byte stored, and at each power up check if any
data has been corrupted. In many apps there is enough
inbuilt eeprom to hold 4x or 8x of each byte.
-Roman

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