View Full Version : Small footprint RAM extension

03-27-2009, 05:00 PM
Hi ... just want to share a finding.

I found these neat FM24Lxxx and FM25Hxx datasheets. It's·FRAM from Ramtron.
FM24Lxxx is available with up to 256kbit@3.3V (mailto:256kbit@3.3V) and can directly replace the EEPROM. It not only has read-access at the speed of 1Mhz it also allows write with the same speed. So, having the usual EEPROM and one of those using different adresses but using the same pins would be a very small footprint RAM extension for the propeller.

FM25Hxx is available with up to 2Mbit and has an SPI that allows 40MHz read AND WRITE. For the propeller that would be full speed access, wouldn't it?

Now think about having several of those chips in parallel. E.G. 8x FM24Lxxx sharing one clock. So, with 9 I/Os you have access to 256kByte FRAM at a data-rate of 8Mbyte/sec (ok, minus some protocoll overhead). But that's nice, isn't it?

I hope that I find a distributor here in germany that sells to private persons as well.

Ken Peterson
03-27-2009, 05:17 PM
That would be rather interesting trying to do 8 I2C interfaces in parallel...http://forums.parallax.com/images/smilies/rolleyes.gif

·"I have always wished that my computer would be as easy to use as my telephone.· My wish has come true.· I no longer know how to use my telephone."

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03-27-2009, 05:19 PM
Look at Tim Moore's SPI SRAM code for multi-bit examples: http://obex.parallax.com/objects/346/


Propalyzer: Propeller PC Logic Analyzer (http://www.brouhaha.com/~sdenson/Propalyzer)
http://forums.parallax.com/showthread.php?p=788230 (http://forums.parallax.com/showthread.php?p=788230)

03-27-2009, 05:41 PM
Thanks jazzed, the N256S0830HDA is for sure an alternative for RAM extension (which doubles my chance to find a distributor for some kind of serial RAM ;o) And of course the driver will be usefull for the SPI devices.

I like the idea to have non volatile RAM. For battery driven devices you can suspend the whole memory to RAM and simply continue where you stopped after wakeup - without the fear of failing EEPROM cells. During operation you can switch off the power for the FRAMs as long as the RAM is not needed.

03-28-2009, 12:46 AM
Just had a look at a FM25H20 data sheet. Another advantage they have is that they stand 1014 read-write-cycles. The disadvantage is the price. At mouse you have to pay more than $25.-- for a single chip. I would think about two an external RAM and an additional nonvolatile memory for poser down.

Airspace V - international hangar flying!
www.airspace-v.com/ggadgets (http://www.airspace-v.com/ggadgets) for tools & toys

03-28-2009, 02:49 AM
If we buy a lot they might get cheaper in the future.

Oldbitcollector (Jeff)
03-28-2009, 05:19 AM
Now we need a video driver which will take advantage of one or more of these options. :)


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03-28-2009, 05:49 AM
to bad there is no regular serial ram greater then 256k. Was trying to find a 4MBit but flash was the only serial option.

Need to make your prop design easier or secure? Get a PropMod (http://propmodule.com) has crystal, eeprom, and programing header in a 40 pin dip 0.7" pitch module with uSD reader, and RTC options.