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EEPROM or NVSRAM

M

mpm

Jan 1, 1970
0
A project I'm working on will likely go into the 1,000's of units.
The design calls for an 8051 and a RTC.

I was planning to use the DS1307 because I'm familiar with it, it fits
the bill, and I already have the code for it. Plus, it's pretty
bullet-proof.

And even though we've used it in lots of prior projects, we never
really had a need to use the skimpy 56 bytes of NV-SRAM it provides.

This project happens to be a candidate. If these bytes didn't exist,
we'd probably just select a micro with EEPROM and that'd be it, or use
an outboard serial EEPROM. (This app does not require so many writes
as to wear out an EEPROM. We're just storing some options variables,
that the user can modify on initial installation.)

So my question: Is there any reason we shouldn't use the DS1307
registers for long-term, unattended memory storage? Anybody doing
this now? And having good results? I would really like to save the $
$ on the less-capable 8051's. (i.e., without EEPROM capability).

We're decided on a CR2032 coin cell, and the 106K holder from Keystone
(which is a FANTASTIC holder for this battery! Nice and tight!) The
battery should last for many years, and it's not a problem if the
memory dumps when replacing the cell.

The application will be inside a work truck, permanently attached, so
bumps and bruises are expected... I should also mention that even if
the memory is lost, the device will still work, but will do so in a
factory-default sort of way - which will likely not be that
objectionable to the customer.(?)

Anybody have any thoughts about EEPROM vs. NV-SRAM or does it really
make any difference?
 
R

Rich Grise

Jan 1, 1970
0
So my question: Is there any reason we shouldn't use the DS1307
registers for long-term, unattended memory storage? Anybody doing this
now? And having good results? I would really like to save the $ $ on
the less-capable 8051's. (i.e., without EEPROM capability).

Well, this part is a little confusing - if you're saying that the uP
without the EEPROM is cheaper than the one with, and you've already
climbed the learning cliff on the DS part, I'd say do it the way you
know.

Before there was flash/eeprom, that's what they did in PCs for some
time.

I once made $60.00 telling a client that their Compaq battery was dead. :)

Cheers!
Rich
 
M

mpm

Jan 1, 1970
0
Well, this part is a little confusing - if you're saying that the uP
without the EEPROM is cheaper than the one with, and you've already
climbed the learning cliff on the DS part, I'd say do it the way you
know.

Micros with EEPROM capability are bit more rare & expensive.
I'm talking about data storage, not program storage. (But I guess
there are some Flash micro's out there that give you in-application
byte-level programming access to the array too. I hadn't even
considered that - and probably wouldn't.)

I guess when you boil it down, it's the "S" in NV-SRAM that's giving
me pause.

It just doesn't sound "reliably permanent", but I guess it keeps time
OK, and it's the same basic memory array, so maybe I shouldn't have
heart palpatiation over it??...
 
R

Rich Grise

Jan 1, 1970
0
Micros with EEPROM capability are bit more rare & expensive. I'm talking
about data storage, not program storage. (But I guess there are some
Flash micro's out there that give you in-application byte-level
programming access to the array too. I hadn't even considered that - and
probably wouldn't.)

I guess when you boil it down, it's the "S" in NV-SRAM that's giving me
pause.

It just doesn't sound "reliably permanent", but I guess it keeps time OK,
and it's the same basic memory array, so maybe I shouldn't have heart
palpatiation over it??...

AFAIK, "SRAM" means "static RAM". So it will be permanent as long as the
battery holds up. And if you're finicky about maintaining it while
changing out the battery, a BMF cap should do it.

Good Luck!
Rich
 
J

Jasen

Jan 1, 1970
0
A project I'm working on will likely go into the 1,000's of units.
The design calls for an 8051 and a RTC.

I was planning to use the DS1307 because I'm familiar with it, it fits
the bill, and I already have the code for it. Plus, it's pretty
bullet-proof.

And even though we've used it in lots of prior projects, we never
really had a need to use the skimpy 56 bytes of NV-SRAM it provides.

This project happens to be a candidate. If these bytes didn't exist,
we'd probably just select a micro with EEPROM and that'd be it, or use
an outboard serial EEPROM. (This app does not require so many writes
as to wear out an EEPROM. We're just storing some options variables,
that the user can modify on initial installation.)

So my question: Is there any reason we shouldn't use the DS1307
registers for long-term, unattended memory storage?

Isn't that exactly what the IBM PC/AT did ?
Anybody doing this now? And having good results?

every time the battery goes flat the configuration goes south.
will that be an issue?

Bye.
Jasen
 
M

mpm

Jan 1, 1970
0
Thanks guys.

After researching this a bit more, and sleeping on it.....

I'm just going to go with storing the user data in the DS1307
registers.
It's the cheapest approach, and the damage done if the data gets lost
or corrupted in insignificant. And the battery change problem isn't a
deal-breaker.

Last couple years I guess was on this flash bandwagon and forgot how
to jump off.....
You start thinking of "static" in terms of minutes, not years.

-mpm
 
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