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PICList Thread
'[PIC]: Eeprom'
2001\01\26@034629 by Francois Robbertze

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Dear PicList Members

Are there a limit to to read/write operations to a pic16f84... in other words, can I read/write to Eeprom say 4 times per second to "save" the status of my pic actions in case of a power failure so that the pic can left of where it stoped? Will the lifetime of the pic be reduced?

For example if I have a action that was switched on  at 10H00 and must switch of at 10H30. Say there are a power failure from 10H05 to 10H06. I want the pic - after reset - to switch the action back on if the stop time was not reached. If there was no flag saved in Eeprom that tells the pic to start the action again the action will be ignored untill the following start time.

I ass-u-me that a write to Eeprom at the instant when the power fails can give unexpected results. How can one get around this? (without the use of a UPS or backup power)

Regards

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|   Francois Robbertze    |
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2001\01\26@080859 by Petra Weeks

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Hi Francois
Without looking at the data sheets, I couldn't give you a precise figure,
but there is a limit to the number of times that you can write to the EEPROM
without errors and at 4 x per second, that would not take long.

I'm sure you would be better off using a battery, back-up, and has the
advantage of keeping a track of the time.

Also a write to EEPROM has a time penalty, and may possibly use up a lot of
your processing time, leaving little room for other things.

Have a look through the components catalogues for suitable devices, and data
sheets and application notes are fairly plentiful.

Maybe some one else out there has a good design ?

With best regards,
Petra.


{Original Message removed}

2001\01\26@083653 by Olin Lathrop

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>>
Are there a limit to to read/write operations to a pic16f84... in other
words, can I read/write to Eeprom say 4 times per second to "save" the
status of my pic actions in case of a power failure so that the pic can left
of where it stoped? Will the lifetime of the pic be reduced?
<<

Yes.  The lifetime of the EEPROM is specified by the number of write cycles.
For example, if the EEPROM is rated at 1,000,000 writes and you do 4 every
second, then the EEPROM could fail in less then 3 days.

If you need this kind of feature, you could try an external battery backed
CMOS static RAM, or arrange for the PIC itself to be battery backed and
asleep when the unit is "off".


*****************************************************************
Olin Lathrop, embedded systems consultant in Devens Massachusetts
(978) 772-3129, olinspamKILLspamembedinc.com, http://www.embedinc.com

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2001\01\26@092737 by Bob Ammerman

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You can often reduce the number of writes dramatically be using some simple
techniques:

1: spread the writes around. don't do all your writes to one location. this
can require some tricky code to figure out what data is the newest.

2: don't write when you don't have to. if the value hasn't changed, don't
write it again.

Bob Ammerman
RAm Systems
(contract development of high performance, high function, low-level
software)

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2001\01\26@100710 by mike

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On Fri, 26 Jan 2001 08:29:21 -0500, you wrote:

>>>
>Are there a limit to to read/write operations to a pic16f84... in other
>words, can I read/write to Eeprom say 4 times per second to "save" the
>status of my pic actions in case of a power failure so that the pic can left
>of where it stoped? Will the lifetime of the pic be reduced?
><<
>
>Yes.  The lifetime of the EEPROM is specified by the number of write cycles.
>For example, if the EEPROM is rated at 1,000,000 writes and you do 4 every
>second, then the EEPROM could fail in less then 3 days.
>
>If you need this kind of feature, you could try an external battery backed
>CMOS static RAM, or arrange for the PIC itself to be battery backed and
>asleep when the unit is "off".
..or use a power-fail detect circuit to do a save-on-powerdown. You
don't need a very big capacitor to run the PIC for long enough to
ensure a safe eeprom write.
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'[PIC]: EEPROM'
2001\12\06@161606 by Gary silva
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Dose anyone have C code for 24LC01B EEPROM?

Gary--

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2001\12\06@234648 by Dale Botkin

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Which compiler?  CCS comes with a driver for it in the drivers
directory...

Dale
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On Thu, 6 Dec 2001, Gary silva wrote:

{Quote hidden}

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2001\12\07@125123 by Carlos Ojea

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You can get some code for a eeprom using Master mode I2C in the appendix 1
of PIC18C Reference guide.
Is this what you need ?


{Original Message removed}

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