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young
Joined: 24 Jun 2004
Posts: 285
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| what is the maximum eeprom available in the market? |
 Posted: Fri Aug 19, 2005 8:28 am |
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| I am looking for a big eeprom memory and related drivers to save data on it using 16f877a, any idea please? |
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mcafzap
Joined: 07 Sep 2003
Posts: 46
Location: Manchester, UK
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| Posted: Fri Aug 19, 2005 9:00 am |
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Microchip does a 512K byte device, the part number escapes me.
Do you really need EEPROM? If you don't need to write 100,000's of times, there are much bigger flash parts, but from your question I presume you've already chosen.
On the same sort of lines, have you noticed how small the largest serial RAM parts are?
HTH
Steve |
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asmallri
Joined: 12 Aug 2004
Posts: 1634
Location: Perth, Australia
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| Posted: Fri Aug 19, 2005 9:03 am |
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| mcafzap wrote: | | Microchip does a 512K byte device, the part number escapes me. Steve |
24LC512
_________________
Regards, Andrew
http://www.brushelectronics.com/software
Home of Ethernet, SD card and Encrypted Serial Bootloaders for PICs!! |
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Guest
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| Posted: Fri Aug 19, 2005 9:30 am |
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thank you mcafzap & asmallri:
I had explored this 24c515 eeprom, what you mean by "much bigger flash parts" I would be glad to know other options! |
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sseidman
Joined: 14 Mar 2005
Posts: 159
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Guest
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| Posted: Fri Aug 19, 2005 10:48 am |
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Thank you sseidman:
will flash memory lose data after power off? how to implement this flash memory with PIC? |
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Mark
Joined: 07 Sep 2003
Posts: 2838
Location: Atlanta, GA
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Fri Aug 19, 2005 11:49 am |
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| Quote: | Microchip does a 512K byte device, the part number escapes me.
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It's 512K bits (64 KB). |
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treitmey
Joined: 23 Jan 2004
Posts: 1094
Location: Appleton,WI USA
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| Posted: Fri Aug 19, 2005 12:33 pm |
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I'm using FRAM, the ramtron FM24C256. It has 32768 Bytes. And superfast. no battery backup and 8 chips connected at the cost of only 2 lines. sda & scl.
8x32768=262144 |
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ckielstra
Joined: 18 Mar 2004
Posts: 3680
Location: The Netherlands
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| Posted: Fri Aug 19, 2005 3:11 pm |
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| Quote: | | will flash memory lose data after power off? how to implement this flash memory with PIC? |
FLASH memory is similar to EEPROM and is sometimes called flash EEPROM, it will hold data without power suppply.
Main differences are that flash needs less transistors per bit which makes it cheaper and results in higher bit capacities per package. A disadvantage of flash is the smaller number of maximum write cycles (typical 100.000 times). Another difference is that in most EEPROMs you can erase/modify a single byte while in FLASH you can only erase whole blocks of multiple bytes (block size depends on manufacturer/model).
FRAM is a new memory type: very fast, unlimited write cycles, write/erase single bytes.
EEPROM: max capacity about 1 Mbit/128kbyte, 1.000.000 write cycles.
FLASH: single chip, about 1Mbit/128kbyte max. In MMC package 2GByte max., 100.000 write cycles.
FRAM: About 1Mbit/128kbyte max. Very fast, unlimited write cycles.
For MMC you will find several links and example code on this forum.
Just one more important note on Flash memory and PIC processors: In flash you can only erase whole blocks, so in order to change a single byte you first read the block, erase the block and write back the updated block of data. In MMC cards the smallest block size is 512 bytes, make sure your PIC has enough RAM available (the 16F877A doesn't). Reading of a single byte is possible, only the write poses this problem. In my system I solved this by adding a small FRAM memory as cache memory, as soon as 512 bytes of data are collected I copy this from FRAM to FLASH (hint: don't place the both devices on the same SPI bus, this won't work because the chip-select line must stay active during the whole write period). |
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Jerry I
Joined: 14 Sep 2003
Posts: 96
Location: Toronto, Ontario, Canada
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| Re: what is the maximum eeprom available in the market? |
| Posted: Fri Aug 19, 2005 4:01 pm |
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| young wrote: | | I am looking for a big eeprom memory and related drivers to save data on it using 16f877a, any idea please? |
 If you use SPI eeprom Microchip now has one 25lc1024 1 Meg
Unfortunately Digikey has a listing but no stock. I think Atmel also makes one.
There is ST Electronics M25P40-VMN6T 3volt Flash 4Meg in 8 pin device same layout as standard Microchip SPI eeproms, they also make smaller 2meg 1meg.
Lots of stock available at digikey and cheaper too.  |
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