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DDR2 chip how slow can you go?
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JohanHoltby:
Hi
I'm investigating how to store a lot of data. and need an as cheap as possible data storage solution. Flash is not an option since I will write it over multiple times every minute.

I'm lookng att an DDR2 chip but since I'm using a low voltage STM32 device which only has a clock speed of about 72mhz. How slow can I go without any problem?

The chip has auto refresh so that will be handled by the ship itself. Cost is a factor so going to SRAM is not an too intresting option if I can get away with using DDR2 chips.


The chip is: W971GG6SB-25-ND
https://www.digikey.se/product-detail/sv/winbond-electronics/W971GG6SB-25/W971GG6SB-25-ND/5125232
amyk:
The datasheet shows a maximum clock period of 8ns, or 125MHz as the minimum speed at which they guarantee it to work.  In practice I believe this is limited by the leakage of the dynamic logic used within, which is related to operating temperature.  This means that it may be possible to go lower if you don't let the temperature go up too high, but I suspect you'll encounter a lot of part-to-part variance.
wraper:
Wait, are you going to bit bang DDR2?  :wtf:.
T3sl4co1l:
What overall lifetime do you want?

Flash at that rate isn't bad if you have tens of gigs to spare.  Shove in an uSD and be done?

You may also consider buffering incremental changes in SRAM or FeRAM, then dumping larger payloads into Flash much less frequently (minutes, hours even?).

Tim
jbb:
It costs more per bit than commodity, but Cypress and Winbond (and some others) have SDR SRAM still very much in production. This should be compatible with the STM32 external memory interface.
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