Cheap, fast, non-volatile memory?

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New product will have multiple axes of motion and nothing but
quadrature encoders and home flags on all but one of them, that is
most axes have no absolute position indicator of any kind.  Adding
expensive absolute position encoders is not an option, cheap ones like
potentiometers with A/D converters are out for reliability reasons.

So on a power-up, the motion control system has no way of knowing for
sure where most axes are.

Once the system has homed all the axes, positions will be kept updated
by the quad encoders some number of times per second, but I'm
concerned about the situation at power-up.  If I could could
continuously capture the latest position updates in non-volatile
storage, I'd have a reasonable starting point after power is cycled.

EEPROM or flash do not seem fast enough to keep up in real time, and
life span could be an issue.

In another product some years ago we used a combination RAM/EEPROM
chip that looked like an 8-bit wide static RAM, but had built-in power
monitoring circuitry.  Given a slow enough fall time on the power
supply, it automatically write protects itself and shadows the RAM
into EEPROM when power goes off, then copies the EEPROM back into RAM
at power-up.  No processor overhead whatsoever.

I could use something like that, but I was wondering if anyone else
has suggestions for something that has reasonable RAM access times
under ordinary circumstances, but transparently preserves stored
values without power.

I'd only need something with a few hundred bytes of storage.  I'd like
to find something in the $5.00 USD range (500 - 1K quantities), but I
could probably go up to $10.00 for the right part.

All suggestions gratefully accepted.

--
Jack Klein
Home: http://JK-Technology.Com
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Re: Cheap, fast, non-volatile memory?
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 Look at RAMTRONs FRAM parts, no write delays and choice of
serial or parallel.

 Any storage could still have granularity issues at power-fail, as
you'll be writing many bytes, and what if part way through the
group update ?
 A group-alternate plus checksum may be needed, or a good early
fail warning flag.

-jg

Re: Cheap, fast, non-volatile memory?
Take a look at ST's non volatile ram (there are other makers also). Mouser
Electronics (Moser?) shows them in their catalog. These are normal ram
devices with a battery included in the package.

Hul

: New product will have multiple axes of motion and nothing but
: quadrature encoders and home flags on all but one of them, that is
: most axes have no absolute position indicator of any kind.  Adding
: expensive absolute position encoders is not an option, cheap ones like
: potentiometers with A/D converters are out for reliability reasons.
:
: So on a power-up, the motion control system has no way of knowing for
: sure where most axes are.
:
: Once the system has homed all the axes, positions will be kept updated
: by the quad encoders some number of times per second, but I'm
: concerned about the situation at power-up.  If I could could
: continuously capture the latest position updates in non-volatile
: storage, I'd have a reasonable starting point after power is cycled.
:
: EEPROM or flash do not seem fast enough to keep up in real time, and
: life span could be an issue.
:
: In another product some years ago we used a combination RAM/EEPROM
: chip that looked like an 8-bit wide static RAM, but had built-in power
: monitoring circuitry.  Given a slow enough fall time on the power
: supply, it automatically write protects itself and shadows the RAM
: into EEPROM when power goes off, then copies the EEPROM back into RAM
: at power-up.  No processor overhead whatsoever.
:
: I could use something like that, but I was wondering if anyone else
: has suggestions for something that has reasonable RAM access times
: under ordinary circumstances, but transparently preserves stored
: values without power.
:
: I'd only need something with a few hundred bytes of storage.  I'd like
: to find something in the $5.00 USD range (500 - 1K quantities), but I
: could probably go up to $10.00 for the right part.
:
: All suggestions gratefully accepted.
:

--
- for email, put the word "keep" in subject line -

Re: Cheap, fast, non-volatile memory?
Simtek make parts like the one you referred to (RAM with automatic EEPROM
backup), They are around $5 for the small ones (www.arrow.com and search for
parts starting STK).

Note the previous poster's comments about incoherent storage if multiple
bytes are involved - you'll need double storage with a checksum or something
to be sure you always have at least one valid position in memory.

Another thing - what if someone pushes your machine when the power's off ?

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Re: Cheap, fast, non-volatile memory?
On Thu, 04 Sep 2003 04:27:04 GMT, "Gary Pace"

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Actually, the part I described that we use in another product was from
Simtek.  I posted from home and just couldn't remember the
manufacturer's name.

--
Jack Klein
Home: http://JK-Technology.Com
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Re: Cheap, fast, non-volatile memory?

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You can put a supercap into your circuit, and in case of a
powerfailure it should give you more than enough time to save
the important data.   In the case of our product (a handheld
device, 4 times the size of a usual remote control) it can be
alive for at least 15 minutes on the built in supercap.



Re: Cheap, fast, non-volatile memory?

Have a look at "FRAM" made by www.ramtron.com.







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Re: Cheap, fast, non-volatile memory?

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     I would agree with the suggestions concerning the use of FRAM.
They are cheaper and simpler than battery backed schemes and write
much faster and with higher endurance (more write cycles) than other
nonvolatile memory.  I have used them in a design and have been very
satisfied.


Re: Cheap, fast, non-volatile memory?
wrote in comp.arch.embedded:

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Thanks, I have.  I haven't gotten prices, but I note that Simtek parts
(which I described but couldn't remember the name) have much faster
access times, down to 25 ns., and are actually quite reasonably
priced.

--
Jack Klein
Home: http://JK-Technology.Com
We've slightly trimmed the long signature. Click to see the full one.

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