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'[PIC]: 16F876 and FLASH memory'
2001\01\26@104745 by Drew Vassallo

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Is it my imagination, or can you take a 16F87X series PIC and, let's say you
only use 1K of program memory, can you use the remaining 7K of program
memory as general RAM storage?  Anyone do this on a regular basis?  I was
going to use an external EEPROM, but because of this feature, I'm thinking I
can just use the unused program memory as NVM RAM... no?  Does this permit
the possibility of generating tables on-the-fly and maintaining the values
after power down?

--Andrew
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2001\01\26@105809 by Drew Vassallo

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Oh, and while we're on the subject, is it possible in MPLAB to limit the
programmer to a certain range of memory locations (e.g. 0-1K) to avoid
programming every unused location with FFFF?  That way, if I only had 500
lines of code in an 8K device, it would go a little faster.  Good for
prototyping/testing sections of code if it worked.

--Andrew
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2001\01\26@114342 by M. Adam Davis

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Drew Vassallo wrote:
> Is it my imagination, or can you take a 16F87X series PIC and...use the
> remaining...program memory as general RAM storage?

Yes, but the flash is only rated to 1000 writes.  I wouldn't use it as
regular ram unless the values didn't change more than a few times a week.

> Anyone do this on a regular basis?

Yes, this is good for infrequently changed values.

> I was
> going to use an external EEPROM, but because of this feature, I'm thinking I
> can just use the unused program memory as NVM RAM... no?  Does this permit
> the possibility of generating tables on-the-fly and maintaining the values
> after power down?

Yes.

> Oh, and while we're on the subject, is it possible in MPLAB to limit the
> programmer to a certain range of memory locations (e.g. 0-1K) to avoid
> programming every unused location with FFFF?

Yes, I do this with my '876s (they take awhile to program if I don't).
Once you start the picstart programmer (enable it), go back up to the
picstart menu, and select the program option.  the programming window
comes up, but it doesn't start programming.  Put the range you want to
program into the boxes, and hit 'program'.

Much faster.

-Adam

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2001\01\26@125112 by Olin Lathrop

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> Is it my imagination, or can you take a 16F87X series PIC and, let's say
you
> only use 1K of program memory, can you use the remaining 7K of program
> memory as general RAM storage?

Yes, but:

1 - The FLASH program memory is optimized differently and is specified for
significantly lower number of lifetime writes.

2 - The whole processor goes out to lunch while the program memory is being
written.

This method is therefore appropriate for an occasional firmware upgrade, new
calibration tables upload and the like.  It is certainly not a substitute
for RAM that is frequently re-written.


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

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2001\01\26@174524 by Bob Ammerman

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----- Original Message -----
From: Drew Vassallo <snurplespamspam_OUTHOTMAIL.COM>
To: <@spam@PICLISTKILLspamspamMITVMA.MIT.EDU>
Sent: Friday, January 26, 2001 10:47 AM
Subject: [PIC]: 16F876 and FLASH memory


> Is it my imagination, or can you take a 16F87X series PIC and, let's say
you
> only use 1K of program memory, can you use the remaining 7K of program
> memory as general RAM storage?

No,  but you can use it as EEPROM storage.

> Anyone do this on a regular basis?

Yep.

> I was
> going to use an external EEPROM, but because of this feature, I'm thinking
I
> can just use the unused program memory as NVM RAM... no?

Again, as EEPROM

>  Does this permit
> the possibility of generating tables on-the-fly and maintaining the values
> after power down?

Sure

But, but two caveats:

1: Write endurance on program "flash" is much less than an data "eeprom"

2: When writing to program "flash" your program is at a complete standstill.

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

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2001\01\27@093540 by dre Domingos F. Souza

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>Yes, but the flash is only rated to 1000 writes.  I wouldn't use it as
>regular ram unless the values didn't change more than a few times a week.

       BTW, is there a I2C RAM?


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