FRAM

alexz · Joined: 17 Sep 2004 Posts: 133 Location: UK

I have noticed, a lot of people in this forum recomend using FRAM.
If I am looking for a fast external memory (not necessarily non volatile) about 128Mbytes capacity, would it be better to consider the FRAM or SRAM?

I am also not sure if FRAM can be that size
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Alex

Ttelmah · Guest

Neither technology is going to give you 128MB, on a single chip, or even that close. The largest normally used SRAM chips are about 8Mb. The biggest readily available, is about 60Mb (not MB). The big question is how fast it needs to be?. the cheapest/easiest way of implementing such a quantity of memory, is to use something like an MMC/SD card, but then write speeds will be slow. However if the need is only for occassional fast 'bursts', you could use a seperate PIC to buffer the request into it's own RAM, and then write the data slowly to the MMC card. Similarly, many CF cards, have buffers, and could be used the same way.
For 128MB of geneal purpose fast memory, I'd suggest just getting an embedded PC chipset, and using SDRAM. It'll be cheaper/easier than trying to implement this amount of memory on a PIC, unless you can use slower technologies...

Best Wishes

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

For that size, I would use mmc. Note that the big sticking point for me with mmc is that they do block read/writes. and you need a large buffer for that data.
...edited..
After seeing Ttelmah msg. I like his idea better. Use the sdram.

asmallri · Joined: 12 Aug 2004 Posts: 1635 Location: Perth, Australia

If you were considering any flash based technolgy, such as SD/MMC//Compact Flash, EEPROM etc then you need to be aware of the maximum number of times a cell can be modified.
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Eugeneo · Joined: 30 Aug 2005 Posts: 155 Location: Calgary, AB

Since you're on this topic, is there any drawback to using a M25P20 (STmicro)... I've built a datalogger that works great at 9600 bps. I've had to setup a 10 byte ring buffer to allow for the slow page writes, but it works very well. It's cheap for 2 mbits of storage. The only drawback I see is it's slow for other certain apps and the erase function is by sector or bulk.