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Question about low frequency SDRAM controller design

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boku

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About SDRAM's CLK

Hello, I'd like to design the sdram controller. After surveying the current SDRAM frequency, the most common is 100/133MHz. What if my design doesn't run in such high freqency. It's only 60 MHz or 30 Mhz in my design. So can I just use low clock freq into SDRAM module's CLK???
Thank you so much!~~~ :roll:
 

ASIC

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Yes it can run at any frequency. I have designed SDRAM controller that runs at 33 MHz and there is no problem. Just make sure you refresh your RAM.


ASIC
 

boku

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Thank you very much. You mentioned about the refresh issue. If the sdram I use is 64ms, 8192-cycles refresh time and my clock freq is 30 MHz, does it mean that the sdram controller needs to refresh every (64,000,000/8,192)ns/(1000/30)ns=234 cycles averagely??
ASIC said:
Yes it can run at any frequency. I have designed SDRAM controller that runs at 33 MHz and there is no problem. Just make sure you refresh your RAM.


ASIC
 

jcss

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Yes. You can issue the auto-refresh command on average 234cycle. At 30MHz, no idle cycle is needed for the precharge (Most SDRAM require ~20ns only) You can also use CL=2. Both can help maximizing the through-put data rate.

Good reference design can be found below: (GPL License)
http://www.cmosexod.com/sdram.html

boku said:
Thank you very much. You mentioned about the refresh issue. If the sdram I use is 64ms, 8192-cycles refresh time and my clock freq is 30 MHz, does it mean that the sdram controller needs to refresh every (64,000,000/8,192)ns/(1000/30)ns=234 cycles averagely??
ASIC said:
Yes it can run at any frequency. I have designed SDRAM controller that runs at 33 MHz and there is no problem. Just make sure you refresh your RAM.


ASIC
 

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