DRAM Question - Auto-Refresh vs. Self Refresh

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faisal78

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difference between auto refresh and self refresh

Hi
I am new to DDR's.
Can somebody help me understand the differences between DRAM auto-refresh function vs. Self Refresh?
It seems that both is internally done by the DRAM...
Can the host processor (DRAM Controller) have anything to do with it?

Is the auto-refresh timing requirement faster better or slower the better?
 

Re: difference between auto refresh and self refresh


So old question, but no answer. This is a question I concern too. I not sure which mode is handled by DRAM Controller, and which mode is handle by SDRAM.

Thanks in advance.
 

Self Refresh:-
The self-refresh operation deactivates the clock to reduce the power consumption of the device, and it automatically executes a refresh operation by using the internal refresh counter. The self-refresh mode is effective when not accessing the device for a long time although the data must be held.

Auto Refresh:-
Auto refresh is a command that refreshes DRAM. When the auto refresh command is input, a row addressNote is selected and refresh is executed. To hold the data, auto refresh must be executed the number of times corresponding to the number of row addresses within the stipulated time for the refresh cycle (tREF). (In the case of 8,192/64 ms, auto refresh must be performed 8,192 times within 64 ms.)
When auto refresh ends, the device automatically goes into the idle status.


Refer This Link
 

Thanks you.

So do you know how to enable Double refresh rate at High temperature.

The description of the DDR datasheet:

At 85~95° TOPER , Double refresh rate(tREFI: 3.9us) is required, and to enter the self refresh mode at this tem-
perature range, an EMRS command is required to change internal refresh rate.


Just enable the High Temperature Self-Refresh Rate by setting EMR2 bit 7 to 1 ?
Do I need to configure tREFI to 3.9us, default is 7.8us ?
 

Re: difference between auto refresh and self refresh

self-refresh mode is nothing but just a standby mode, so that data is not lost when external clock is not there.. it is purely to save power consumption..
Auto-refresh mode auto refreshing of data happens every pre-defined time intervals.. usually a command is there to enter self refreshing mode.
After the SELF REFRESH command is registered, all the inputs to the SDRAM become “Don’t Care” with the exception of clock signal, which must remain LOW.
 
Sorry friend I don't know about the timings. I'll try to figure it out and reply if I get to know about it.
 

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