External Memory

AK · Joined: 20 Apr 2004 Posts: 33

Hello,

I am looking for suggestions on what I should use for external memory with a current project that I am working on. I need to store about 1300 seven character strings or it may end up being 1300 floating point values (format has not been decided). I would prefer not to use a USART since I am already using the hardware USART to communicate with the LCD. Thanks for the help.

Scott

Ttelmah · Guest

Any number of I2C, or SPI memories available. Do the contents need to be saved when power is removed?. How often does the data need to change?. If it needs to be permannent, and the update is not too frequent, with the slow write speed not therefore a problem, an EEPROM, is cheap and easy, with complete libraries already included with the compiler.

Best Wishes

AK · Joined: 20 Apr 2004 Posts: 33

The contents do need to be saved when power is removed. The data for a specific memory location won't change that often. The application basically requires the user to enter data via a touchscreen keypad. The entered data would then be saved. I don't think that speed is a big issue. Is there a specific I2C chip that you would recommend?
Thanks,
Scott

jecottrell · Joined: 16 Jan 2005 Posts: 559 Location: Tucson, AZ

Take a look at this page. The I2C devices are at the top.

http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=80

They allow for up to 8 devices on the same bus and I think all the different capacities are pin compatible.

I've gotten into the habit of throwing one on to each design, just in case I might need it.

Drivers are available in the examples or in the forums.

Good Luck,

John

treitmey · Joined: 23 Jan 2004 Posts: 1094 Location: Appleton,WI USA

I like the FRAM's from ramtron. FM24C256 is I2C. They hold data in power outage without battery. 8 chips addressable. 32768byte/chip for a total of 265k byte. I use them on hardware I2C using fast setting.
These have a fast write time.(faster than s-eprom)
[[NO WAITING]]

I also throw 1 on the board just in case I need it.
http://www.ramtron.com/lib/literature/datasheets/FM24C256ds_r3.1.pdf

jecottrell · Joined: 16 Jan 2005 Posts: 559 Location: Tucson, AZ

I looked at the data sheet for the FRAM. 5V only, be careful if you're doing low power stuff.

Also, Couldn't find a source. Then I noticed that there was a recent thread on that topic.

So it looks like FRAM has speed....

And EEPROM has low power and availability.

How does FRAM compare in cost?

Thanks,

John

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

What about this chart here ? It says 2.7-3.6v for several chips:
http://www.ramtron.com/doc/Products/serial.asp

jecottrell · Joined: 16 Jan 2005 Posts: 559 Location: Tucson, AZ

I stand corrected. (I missed the product matrix on the web page.)

How about price? How does it compare?

Thanks,

John