Searching \ for ' SRAM versis DRAM' in subject line. ()
Make payments with PayPal - it's fast, free and secure! Help us get a faster server
FAQ page: www.piclist.com/techref/mems.htm?key=sram
Search entire site for: 'SRAM versis DRAM'.

No exact or substring matches. trying for part
PICList Thread
'[PICLIST] SRAM versis DRAM'
2002\04\22@191630 by Benjamin Bromilow

flavicon
face
Hi all,

I'm looking for some *relatively* large memory (eg around 1M)
As I see it, DRAM has the advantage of fewer pins but the disadvantage of
needing refreshing. SRAMs need more pins (nothing a multiplexer or a 16F877
can't solve), but seem to be much much cheaper. I was amazed at how much
the DRAMs where for a similar storage capacity. Why then would anyone therefore
use DRAMs?? Am I missing something?

Ben

--
http://www.piclist.com hint: PICList Posts must start with ONE topic:
[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads


'[PICLIST] [EE] RE: SRAM versis DRAM'
2002\04\22@193013 by John Dammeyer

flavicon
face
At one time 1M dynamics were much less expensive compared to static
RAMs.  That's when the idea of more than 1MByte in a PC was considered
absurd.  If you want to put a SIMM into a PIC you need to think 16Mbyte
minimum and then you can get the SIMMs for under $50.  What a PIC would
do with that much memory I'd love to hear about.

John


> {Original Message removed}

2002\04\22@194654 by Mark J. Dulcey

flavicon
face
Benjamin Bromilow wrote:
> Hi all,
>
> I'm looking for some *relatively* large memory (eg around 1M)
> As I see it, DRAM has the advantage of fewer pins but the disadvantage of
> needing refreshing. SRAMs need more pins (nothing a multiplexer or a 16F877
> can't solve), but seem to be much much cheaper. I was amazed at how much
> the DRAMs where for a similar storage capacity. Why then would anyone therefore
> use DRAMs?? Am I missing something?

DRAMs tend to be ridiculously expensive when bought in small quantities,
because nobody buys them that way. The people who buy DRAM chips
purchase them in very large quantities (tens of thousands and up). Small
users are typically buying their DRAM in the form of things like memory
modules, not buying chips directly from the manufacturers.

Furthermore, a measly 1Mbit chip is a very SMALL one by current DRAM
standards; it's hopelessly obsolete. (About the smallest DRAM chip that
will actually find its way into a PC these days, for instance, is
64Mbits.) So you're paying a premium for buying something that they're
only reluctantly keeping in the product line at all, for the sake of
people who need them to repair old equipment.

Note that I stated the sizes above in megaBITS, not megaBYTES; convert
if needed.

Most gadgets that need only a small amount of RAM (and 1 meg is a small
amount now) use SRAM because it's easier to work with; no refresh to
worry about, and no critical row/column timing. But DRAM is cheaper when
you want a LOT of memory. Just compare the price of 256 megabytes of
SRAM chips to the price of a 256MB DIMM. The largest SRAM chip currently
in the Digi-Key catalog, for instance, is a Toshiba 8Mbit (512Kx16)
SRAM; in other words, one megabyte. It costs $20 in quantity 500, and
not much less in quantity 5000. To make 256 MB, you would need 256 of
them, for a total cost of over $5,000. You can buy a 256MB DIMM for
under $100 in quantity one; a 256MB DDR SDRAM non-parity DIMM sells for
$85.49 on crucial.com.

But suppose you only need one megabyte? The smallest module currently
available from Crucial is a 32 megabyte module; it sells for $20.69,
which is right around the same price as the 1 megabyte Toshiba chip, and
it will hook up to your microprocessor with less glue and less hassle[.
And if need less than a megabyte, you can buy a smaller SRAM chip
(Digikey offers a 4MB Toshiba chip that is about half the price of the
8MB), but you've bottomed out on the DRAM options.

--
http://www.piclist.com hint: PICList Posts must start with ONE topic:
[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads


2002\04\22@195717 by Tony Nixon

flavicon
picon face
"Mark J. Dulcey" wrote:

> But suppose you only need one megabyte? The smallest module currently
> available from Crucial is a 32 megabyte module; it sells for $20.69,

Any more details on this module?

--
Best regards

Tony

mICros
http://www.bubblesoftonline.com
spam_OUTsalesTakeThisOuTspambubblesoftonline.com

--
http://www.piclist.com hint: PICList Posts must start with ONE topic:
[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads


2002\04\22@201238 by Mark J. Dulcey

flavicon
face
Tony Nixon wrote:
> "Mark J. Dulcey" wrote:
>
>
>>But suppose you only need one megabyte? The smallest module currently
>>available from Crucial is a 32 megabyte module; it sells for $20.69,
>
>
> Any more details on this module?

That's just a perfectly ordinary 32 megabyte SDRAM module; if you really
want the details, they're at
http://www.crucial.com/store/PartSpecs.asp?imodule=CT4M64S4D7E.

You probably raised the question because of the following paragraph from
my original post, which, on rereading, came out wrong. What I meant to
say is "the SRAM will be easier to connect", not that the module would be.

On the other hand, if you really do need 32 megabytes of memory in a
microcontroller project, an SDRAM module is probably just the thing. And
you probably don't even have to spend $20 for a new one; just find
somebody who recently upgraded his PC, and you can probably get one for
free or nearly free.

One concept I'm planning to play with someday is a digital storage
oscilloscope. I might have it interface to a PC (parallel port or USB)
as the output device, or perhaps put a graphic LCD on the thing. I'd use
DRAM for the memory; one appealing thing in this application is that
there is no refresh hassle at all, because the normal operation of the
thing will cycle through the memory sequentially! Way back in Ye Olden
Daisies, the Apple ][ used the same trick; it didn't need any refresh
circuitry, because the normal operation of the video display kept the
RAM happy.

> But suppose you only need one megabyte? The smallest module currently
> available from Crucial is a 32 megabyte module; it sells for $20.69,
> which is right around the same price as the 1 megabyte Toshiba chip, and
> it will hook up to your microprocessor with less glue and less hassle[.
> And if need less than a megabyte, you can buy a smaller SRAM chip
> (Digikey offers a 4MB Toshiba chip that is about half the price of the
> 8MB), but you've bottomed out on the DRAM options.

--
http://www.piclist.com hint: PICList Posts must start with ONE topic:
[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads


2002\04\23@060957 by Mahmood Elnasser

flavicon
face
I think its silly using 32MB ram on a microcontroller, its simple maths
you need 25 I/o lines for addresses bus Plus 3 control lines + 8 data
lines which takes 36 I/O pins.
Very few microcontrollers have enuf pins for that.
{Original Message removed}

More... (looser matching)
- Last day of these posts
- In 2002 , 2003 only
- Today
- New search...