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'[PICLIST] (PIC): 16F877 -- Why an EEPROM?'
2001\03\05@172741 by Barnaby Thieme

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Hello.  
I'm considering moving from the PIC 16C65B and PIC 16C67 to a FLASH memory microcontroller.  I've been looking at the 16F877 and I can't really figure out why anyone would need an EEPROM when apparently it's just as easy to read from and write to the program memory.  Is it a matter of code protection (i.e., no danger of stomping on critical code)?  Any thoughts?

Barnaby Thieme
Product Engineer, SP Controls, Inc.
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2001\03\05@173618 by Mike Mansheim

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> I'm considering moving from the PIC 16C65B and PIC 16C67 to a FLASH
memory
> microcontroller.  I've been looking at the 16F877 and I can't really
figure out
> why anyone would need an EEPROM when apparently it's just as easy to read
from
> and write to the program memory.  Is it a matter of code protection
(i.e., no
> danger of stomping on critical code)?  Any thoughts?

The number of writes allowed is much higher on the data EEPROM.
Per an older F876 data sheet (I assume the F877 is the same):
Endurance for the data EEPROM is 100,000 cycles; endurance for the program
flash
memory is 1000 cycles.

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2001\03\05@174850 by Tony Nixon

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Barnaby Thieme wrote:
>
> Hello.
>
> I'm considering moving from the PIC 16C65B and PIC 16C67 to a FLASH memory microcontroller.  I've been looking at the 16F877 and I can't really figure out why anyone would need an EEPROM when apparently it's just as easy to read from and write to the program memory.  Is it a matter of code protection (i.e., no danger of stomping on critical code)?  Any thoughts?


1,000,000 EEPROM write cycles versus 1,000 (or so) ROM write cycles.

You can't store 2 X 8 bit values in ROM (14 bits only)
Good for storing 2 ASCII bytes though

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2001\03\05@175932 by Gabriel Gonzalez

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EEPROM has more read/write endurance cycles, something like 100,000.

----- Original Message -----
From: Barnaby Thieme <bthiemespamKILLspamSPCONTROLS.COM>
To: <.....PICLISTKILLspamspam.....MITVMA.MIT.EDU>
Sent: Monday, March 05, 2001 3:25 PM
Subject: (PIC): 16F877 -- Why an EEPROM?


Hello.

I'm considering moving from the PIC 16C65B and PIC 16C67 to a FLASH memory
microcontroller.  I've been looking at the 16F877 and I can't really figure
out why anyone would need an EEPROM when apparently it's just as easy to
read from and write to the program memory.  Is it a matter of code
protection (i.e., no danger of stomping on critical code)?  Any thoughts?

Barnaby Thieme
Product Engineer, SP Controls, Inc.
EraseMEbthiemespam_OUTspamTakeThisOuTspcontrols.com

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2001\03\05@181025 by shane

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EEPROM can be written/rewritten thousands of times.  Flash has a limited writing memory, and it is very slow to rewrite program
memory. If the chip is code protected, one cannot write at all to the flash program memory, but one can still use EEPROM memory.

Shane Tolmie
Workingtex
http://www.workingtex.com/htpic for PIC micro and C code with FAQ, source, samples, etc.

> {Original Message removed}

2001\03\05@183454 by Bob Ammerman

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1:    Your program can be doing something else while writing to EEPROM, this
isn't true for program flash.

2:    The write endurance figure for EEPROM is _much_ higher than for
program flash.

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

{Original Message removed}

2001\03\06@133808 by Mike Mansheim

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----- Forwarded by Michael J Mansheim/Graco on 03/06/01 12:36 PM -----

> EEPROM can be written/rewritten thousands of times.  Flash has a limited
> writing memory, and it is very slow to rewrite program memory. If the
> chip is code protected, one cannot write at all to the flash program
> memory, but one can still use EEPROM memory.

Actually, the write cycle times are the same (4 ms typ, 10 ms max) for
both types of memory.

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2001\03\06@140508 by Gabriel Gonzalez

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Why don't they make the whole thing EEPROM???

----- Original Message -----
From: Mike Mansheim <@spam@Michael_J_MansheimKILLspamspamGRACO.COM>
To: <KILLspamPICLISTKILLspamspamMITVMA.MIT.EDU>
Sent: Tuesday, March 06, 2001 11:33 AM
Subject: Re: (PIC): 16F877 -- Why an EEPROM?


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2001\03\06@141744 by Les

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>Why don't they make the whole thing EEPROM???

Cos they don't want their chips to last too long probably. Bad for
business!!!!

On the same note. Why don't they make a flash version of the 8-pin devices?
Probably the same answer as above. They'd lose sales of the non-flash
versions.


Les

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2001\03\06@145823 by James Montebello

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Actually, it's probably all down to cost.  FLASH probably costs more
to make, and the 8-pin devices are esp. sensitive to cost, since they
have to be very cheap or nobody would bother with them.  In other words,
I think they don't make flash versions of the 8-pin devices because they
don't think enough people would pay the price they'd have to charge for
them.

jamesm

On Wed, 7 Mar 2001, Les wrote:

{Quote hidden}

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2001\03\06@165817 by Tony Nixon

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Les wrote:
>
> >Why don't they make the whole thing EEPROM???
>
> Cos they don't want their chips to last too long probably. Bad for
> business!!!!
>
> On the same note. Why don't they make a flash version of the 8-pin devices?
> Probably the same answer as above. They'd lose sales of the non-flash
> versions.
>
> Les

Future products guide lists the 8 pin 18F0x0 and 18F0x2 chips - based on
the 18Cxxx series - upto 10 MIPs.


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2001\03\07@063206 by mike

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On Tue, 6 Mar 2001 12:33:11 -0600, you wrote:

>----- Forwarded by Michael J Mansheim/Graco on 03/06/01 12:36 PM -----
>
>> EEPROM can be written/rewritten thousands of times.  Flash has a limited
>> writing memory, and it is very slow to rewrite program memory. If the
>> chip is code protected, one cannot write at all to the flash program
>> memory, but one can still use EEPROM memory.
>
>Actually, the write cycle times are the same (4 ms typ, 10 ms max) for
>both types of memory.
Except with the eeprom the processor can be doing other things during
the write. Writing the flash halts the CPU for the duration.
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2001\03\07@063208 by mike

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On Tue, 6 Mar 2001 11:47:16 -0800, you wrote:

>Actually, it's probably all down to cost.  FLASH probably costs more
>to make, and the 8-pin devices are esp. sensitive to cost, since they
>have to be very cheap or nobody would bother with them.  In other words,
>I think they don't make flash versions of the 8-pin devices because they
>don't think enough people would pay the price they'd have to charge for
>them.
..and the sort of products that use 8-pin devices are  less likely to
benefit sufficiently from reprogrammability to justify the extra cost.

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