Serial EEPROM advice

duffling

My SX project now requires some storage , and im going to need around 256bytes or more

can someone advise me on some iC to look for?

thanks again.
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Paul Baker

Do you need fast and frequently updated memory or memory that keeps its data with the power turned off and only needs updating ocassionally?

duffling

No speed is not really important at this stage ,i used the BS2p for my test run of this project and the speed of this eerpom was fine ,

i will be moving some small blocks of memory around , usually a word or a byte at a time

I want to seup up something similar to a syntheizers PATCH memory , each patch on my program is going to be around 12 bytes , and i wish to store around 99 of this program blocks in eeprom

for future projects i will need to access faster memory so i guess some info on whats out there would be helpful [noparse]:)[/noparse]

Bean

I think what Paul was getting at, is that EEPROM has a limited number of writes. If this is data that changes every minute, the EEPROM could wear out after a time. Assuming your data isn't going to change much, the SPI interface is probably the easiest to use.

Parallax has an 8K EEPROM, but it's a bit pricy at $10.50, but it has stamp code to use it.
http://www.parallax.com/detail.asp?product_id=602-00008
Bean.

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Paul Baker

Ok seeing as how you didn't list nonvolatility as important, I will point you to a device I just discovered. I suggest getting Phillips PCF8570, this is a 256 byte serial SRAM with I2C interface, availible in 8-dip and·8-SOIC packages, digikey sells them for $3.22·for the dip and $2.48 SOIC, check www.findchips.com to see if there are any cheaper vendors. Here is the spec sheet.

If non-volatility is something you want, then you could get something like Microchip's 25C040. Its a·1 kByte serial SPI EEPROM availible for <$1 at digikey.

You sound like you want something akin to the stamps scratchpad, am I correct? If I am, get the first part mentioned and you wont have to worry about wear-leveling and MTBF rates.

duffling

Well its mainly to store program setups in memory , and i do need it to be retained after power off ,
the programs will be edited and stored in this eeprom

my project does require a small area to move bytes around . along with a storage area for the main programs ..
so really ill be looking at BOTH types..

pjv

Hi Duffling;

Check the thread "Serial Rams" last posted by Paul Baker on March 24 regarding this issue. In my research on the matter, the Ramtron FM25256 (5V) is a good choice; the low voltage (3.3V) version FM25L256 has UNLIMITED read/writes, serial SPI access, and a relatively fast 20MHz clock. It is also available in I2C, but that is such an ugly protocol, I don't know why anyone would ever use I2C if there is another choice. Poking at their website, I see also that parallels are available.

From my persective, the FM25256 with SPI is the only way to go. In fact I'm designing it in on a SX52 general purpose development board similar to my contest entry that I will be selling in the near future. My samples are on the way, and I want confirm my understanding of their operation.

Some of the product variations are stocked by Future.

Cheers,

Peter (pjv)

Paul Baker

Peter, you are correct that the FM25256 is by light years superior. Since it is FRAM (aka MRAM) it is fast, nonvolatile, with practically unlimited number of write cycles. The problem is FRAM/MRAM is an emergent technology and is extremely limited in availibility at this point. The FM25256 is not availible from Future, the FM24C16A and FM24C16A are availible, both are I2C protocol chips and only availible in quantities of 100 or greater. However NewarkInOne has a better supply, including SPI versions in single quanities. I have purchased from them before and was pleased with thier service.