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flash variable erased

 
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lor3nzo



Joined: 19 Jan 2014
Posts: 4

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flash variable erased
PostPosted: Tue Feb 10, 2015 12:33 pm     Reply with quote
I reserved a small flash area of a 18f45k22 to save some variables.
A device returned with this area erased.
How is this possible ?
PCM programmer



Joined: 06 Sep 2003
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PostPosted: Tue Feb 10, 2015 12:50 pm     Reply with quote
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There are many threads on this topic. Here are two of them:
http://www.ccsinfo.com/forum/viewtopic.php?t=40163
http://www.ccsinfo.com/forum/viewtopic.php?t=43035
Ttelmah



Joined: 11 Mar 2010
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PostPosted: Tue Feb 10, 2015 1:25 pm     Reply with quote
as an 'add on' to the threads suggested by PCM_programmer, if you are 'reserving a small flash area to save some variables', have you studied how this has to be done. Flash is _not_ like EEPROM. You can't just write a byte. To change one byte, you have to read an entire _page_ (64bytes on this chip), change the single byte you want to modify, and write the whole page back. A write to the first byte of a page, _will_ erase the whole page.
lor3nzo



Joined: 19 Jan 2014
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PostPosted: Tue Feb 10, 2015 5:23 pm     Reply with quote
When flash erase size is equal to flash write size, bytes outside the range of the write block are not changed. Is this true?
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