Cheap, fast, non-volatile memory?

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

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

Jack Klein wrote: : 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. :

Simtek make parts like the one you referred to (RAM with automatic EEPROM backup), They are around $5 for the small ones

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 ?

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.

Have a look at "FRAM" made by

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.

On Thu, 04 Sep 2003 04:27:04 GMT, "Gary Pace" wrote in comp.arch.embedded:

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.

On Thu, 4 Sep 2003 18:26:55 +1000, "Phil W" wrote in comp.arch.embedded:

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.