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'[PIC]: (was (PIC)) 16F877 -- Why an EEPROM?'
2001\03\06@155329 by Barry King

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

There is a big difference in the chip size for a given amount of
flash or EEPROM.  The flash is much smaller and therefore cheaper.

The advantages of EEPROM are byte-wise reprogrammability (Flash has
to be "bulk" erased, although the flash guys keep adding more sectors
to reduce the size of the erase block)

The other advantage of EE is the endurance.  EE can be built for 1M+
read write cycles, and 100,000 is normal nowadays.

For Flash, there is a design tradeoff between fast programming and
long life, which is usually resolved "as fast as possible with 1000
cycle life".

> 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.

Flash is more complex to build than EPROM (OTP), so I'd speculate
that the MicroChip strategy is to release the new function / pinout
in OTP first and then do a refinement of the CPU (a "B" part) with
the Flash replacing the EPROM.

It also might be a die-size problem.  Since Flash cells are bigger
than EPROM, a chip with Flash program mem. might not fit in the SO-8
package.  It would be nice to make 'em in DIPs, even so.

-Barry.
------------
Barry King, Engineering Manager
NRG Systems "Measuring the Wind's Energy"
http://www.nrgsystems.com
Phone: 802-482-2255
FAX:   802-482-2272

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2001\03\11@021303 by Bill Westfield

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

   There is a big difference in the chip size for a given amount of
   flash or EEPROM.  The flash is much smaller and therefore cheaper.

I keep hearing (and I believe) that the "flash" and "eeprom" in the PIC
parts are actually the same technology (EEPROM, technically speaking.)
Perhaps this is only true for the older (16F84/16C84) chips (where they
actually changed the literature without appearing to change the chip
very much.)  The cost difference you're talking about is what allows
intel/amd/etc flash chips to hold megaBYTES of data - it's pretty
irrelevant in a device with a couple kbytes...

That would mean that the difference between the "flash" and "eeprom" cells
is either one of physical layout (ie eeprom has smaller or larger physical
features resulting in changed behavior) or simply a matter of testing
(clearly it's easier to test 64 bytes of programatically-writable "eeprom"
for large numbers of cycles than to test several Kbytes of "flash" that can
only be written externally...

I can't say much about other (manufacturers) chip famillies.  Somewhere
there's probably a record of who has actually licensed/patented flash
technology vs eeprom technology.  Atmel clearly has both in their product
portfolio - I haven't a clue as to which are used in their micros...

BillW

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2001\03\11@075908 by Timothy Stranex

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Just wondering, why are serial eeproms much cheaper than parallel ones?
is it just that the parallel one need more pins?

Thanks,
Timothy Stranex
timotspamKILLspamuskonet.com

On Sun, 11 Mar 2001, you wrote:
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