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'PIC to change Code as it runs?'
2000\03\30@230610 by Ian Wilkinson

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I've just been reading the documentation on the 16C877, does the part where
it says the PIC can write to the Flash mean that you could get the PIC to
write a data into the flash and then run what the PIC had written as if it
had been programmed in the first place??

And while I'm on the subject can someone explain the difference between
Flash and EEPROM as I can see very little difference (It's been two years
since I've done anything with memory :)

Thanks again.

Ian.


'PIC to change Code as it runs?'
2000\04\03@141216 by Andrew Warren
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Ian Wilkinson <spam_OUTPICLISTTakeThisOuTspamMITVMA.MIT.EDU> wrote:

> I've just been reading the documentation on the 16C877, does the part
> where it says the PIC can write to the Flash mean that you could get
> the PIC to write a data into the flash and then run what the PIC had
> written as if it had been programmed in the first place??

   Yes.

> And while I'm on the subject can someone explain the difference
> between Flash and EEPROM as I can see very little difference

   In the context of non-volatile PIC memory, there IS no
   difference; for marketing reasons, Microchip uses "flash" as a
   synonym for "EEPROM".

   -Andy


=== Andrew Warren - .....fastfwdKILLspamspam@spam@ix.netcom.com
=== Fast Forward Engineering - San Diego, California
=== http://www.geocities.com/SiliconValley/2499

2000\04\03@154447 by Stephan Kotze

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AFAIK you can only write to the flash about a 1000 times wheras the eeprom
has about a 1e6 cycle lifetime. This may have been changed in the latest
PICs

Stephan
{Original Message removed}

2000\04\03@170237 by M. Adam Davis

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FLASH memory is EEPROM memory (ie, electrically erasable), except instead of
erasing each bit (byte, word) seperately/sequentially, you can 'flash' the
entire memory at once.  This takes longer than a single bit/byte/word erase, but
much less time than doing a sequantial erase.

This is referred to a bulk erasing in microchip's literature.  The new PICs can
read and write directly to their own program area, but they cannot perform a
bulk erase (flash) on themselves.  While this would make sense (where does the
program go now that it's erased itself) it would be nice to have for secure data
purposes.

It is possible to write self-modifying code with these PICs.

Alas, like eeprom memory, there is a limited life span, often expressed in how
many times it can be written to before experiencing a bit error (usually greater
than 10 million).

-Adam

Ian Wilkinson wrote:
{Quote hidden}

2000\04\06@035702 by paulb

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Andrew Warren wrote:

> Self-modifying code isn't always a bad thing...
> It's usually used in order to speed the operation of a program.  For
> instance, if you're working with a microprocessor whose literal-
> addressing instructions execute faster than its direct register-
> addressing instructions, a self-modifying program can be used to pre-
> read register contents and plug those numbers into literal-addressing
> instructions.

 It also saves registers in that example.
--
 Cheers,
       Paul B.

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