SDRAM

A read on a row in SDRAM accomplishes a refresh, so if you read all used
rows within the refresh period, you do not need an explicit refresh.  I've
used that in video applications on several occasions.

Tommy Thorn wrote:

> RANGA REDDY wrote:
> > is it true that Micron SDRAM does not require any refresh cycles if we
> > are reading the SDRAM rows once in 20 ms atleast? if i dont give any
> > refresh cycles what will be the condition of the SDRAM?
>
> AFAIK, *no* SDRAM requires refresh cycles if all the rows you care about
> are touched (read or written) sufficiently often.  I think once every
> 64ms is enough.
>
> I've never seen anybody take advantage of that though.
>
> Tommy

--
--Ray Andraka, P.E.
President, the Andraka Consulting Group, Inc.
401/884-7930     Fax 401/884-7950
email ray@andraka.com
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 "They that give up essential liberty to obtain a little
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                                          -Benjamin Franklin, 1759

In article <40C9D4DC.8060900@yahoo.com>, TommyAtNumba-Tu.Com--
not@yahoo.com says...
> RANGA REDDY wrote:
> > is it true that Micron SDRAM does not require any refresh cycles if we
> > are reading the SDRAM rows once in 20 ms atleast? if i dont give any
> > refresh cycles what will be the condition of the SDRAM?
> 
> AFAIK, *no* SDRAM requires refresh cycles if all the rows you care about 
> are touched (read or written) sufficiently often.  I think once every 
> 64ms is enough.
> 
> I've never seen anybody take advantage of that though.

The original IBM PC had one of the DMA channels set up to do periodic 
reads from contiguous locations to the DRAM refresh.

-- 
  Keith