Source for SDRAM chips

Do you have a question? Post it now! No Registration Necessary

Translate This Thread From English to

Threaded View
Does anyone know where small quantities of SDRAM chips (not modules) could be
purchased?

Thanks,
Alex Parkinson

Re: Source for SDRAM chips
Quoted text here. Click to load it
purchased?
yes.

Re: Source for SDRAM chips
Quoted text here. Click to load it

Thank you. That was very helpful.

Re: Source for SDRAM chips
www.digikey.com comes to mind.
www.mouser.com
www.jameco.com
sometimes www.allelectronics.com and or www.bgmicro.com have them in too.
www.ebay.com sometimes has the chips for sale or auction too.


Quoted text here. Click to load it



Re: Source for SDRAM chips
Are you looking for specific chips, or just any parts in approximately
the right density?

I had big trouble trying to source 1Mx16 SDRAMs for an ARM prototype
run we did about a year ago. I eventually cannibalized SODIMMs :(


Re: Source for SDRAM chips
Quoted text here. Click to load it

I'm not looking for any particular chips, mainly just anything at about 1M x 8
and up.

Re: Source for SDRAM chips
Quoted text here. Click to load it

and up.

what happened when you did web searches?
what did you find with mouser, digikey, and other vendors that you found
from your web search?

Re: Source for SDRAM chips
No stock, or minimum purchase a waffle, for every single part number I
could find that was compatible with my design. Mostly it was no stock.
I eventually begged some samples out of Micron, I think.


Re: Source for SDRAM chips
Quoted text here. Click to load it

I haven't found anything with Digikey, Mouser, AvNet, Future, Allied, Newark,
All
Electronics, or BG Micro.  So far Arrow, which was suggested by Richard H.,
seems to be
the only major vendor that sells them in small quantities. I've seen them on
eBay
before, but I'd like to find a source that's a little more reliable.

Re: Source for SDRAM chips
Quoted text here. Click to load it

I'm glad that pointer was useful.  IIRC, I went about it the reverse
direction - asked the manufacturer who stocks their parts and sells qty
1.  In fact, I think I was asking about samples sources.  I stopped when
I found the first one, but you might try this with other manufacturers.

I got the sense that DRAM prices are too volatile for most distributors
to stock...

What quantities are you looking for?  A TSSOP tray looks to be 108 pcs
(~USD$1000 for 32MB chips) - a bit much for hobby, but maybe not for
short-run production.  Distributors might be more willing to broker full
trays.

Also, you might check with smaller shops that make products with similar
parts - they may be willing to sell you loose parts from their
inventory.

Re: Source for SDRAM chips

Quoted text here. Click to load it

I think the main problem is that not many people these days use loose DRAM
chips, as modules are so
widely available - for development quantities, it will often be easier and
cheaper to strip chips
off a PC memory module where possible.

Re: Source for SDRAM chips
If I have to do it again, I think I'll design in a SODIMM socket anyway
(at least for prototypes). Being able to upgrade the RAM ex post facto
is a Good Thing :)


Re: Source for SDRAM chips
Quoted text here. Click to load it

Lewin,

When I last looked into this, I discovered SIMM sockets were very
expensive through the Usual Sources - ballpark USD$25.  Even if the SDR
SIMM was free, the solution was much more expensive than just buying an
oversized chip.  Have you found a source for SIMM & DIMM sockets that's
reasonably priced?

Also, you mention SODIMMs - are you using a DRAM controller?  SDR seems
to be the end of the road without one (timing stability, clock speed,
etc.), but apparently they aren't available as discrete parts anymore -
know of any discrete DRAM controllers?

Richard

Re: Source for SDRAM chips
Hi,

The cheapest I've seen 144-pin SODIMM sockets is on the secondary
market at about $1.50 each. In production quantity of course they are
cheaper than this. Digi-Key sells them at $5.98 qty 1, going down
rapidly with quantity. WM18501-ND is the part#. 64Mb PC66 or PC100
SODIMMs - if you can find them - start at around $10 in surplus
quantities.

I was using ARM devices with on-chip SDRAM controllers, e.g. Cirrus
7312, Sharp LH79520. Async DRAM is virtually a dead product line, no?
If I had to add SDRAM to a micro that didn't have an on-chip
controller, I would either change micros (most likely) or if ABSOLUTELY
necessary I would think about doing the controller in an FPGA.
opencores has an SDRAM controller.


Re: Source for SDRAM chips
Quoted text here. Click to load it

I was thinking about doing this.  Do you happen to know how many gates would be
needed
for a basic SDRAM controller?  I have a project in mind where I'll need to put
an SDRAM
controller (among a few other things) into a cheap CPLD, but at this point I'm
not even
sure if that will be possible.  I don't need to implement all of the
functionality of
the SDRAM - just reads and writes of single locations, as well as refreshing
when necessary.

Re: Source for SDRAM chips
Quoted text here. Click to load it

Not sure that this can be done with a CPLD, at least not without driving
it from the MCU.  My limited knowledge of CPLD and FPGA leads me to
think you'll need an FPGA to make it run autonomously.


Quoted text here. Click to load it

I don't think there's much more, except burst modes for higher
performance I/O.  But refreshing is no small task - it's a huge overhead
to bit-bang without a controller.

See if the SDRAM you're looking at supports self-refresh mode.  I'm not
sure if it's a standard capability, but I know Micron supports an
internal self-refresh that's 'set & forget'.

If you're looking at newer SDRAM technologies, you'll probably have to
use a DRAM controller of some sort because of the tightness and
consistency of the timing specs.  What type of SDRAM are you exploring?

Richard

Re: Source for SDRAM chips
Sorry, programmable logic is not my specialty, but I second Richard in
the belief that you likely can't do it in a CPLD. It's complicated.


Re: Source for SDRAM chips

Quoted text here. Click to load it

I did a SDRAM controller for an AD 2185 DSP and a 1Mx16 SDRAM
in a xilinx 95108 along with some clock generation and DAC
interface logic some while back.  IIRC the cpu handled refresh,
the sdram was run at 33 Mhz cas latency 1.

Re: Source for SDRAM chips
Quoted text here. Click to load it

Thanks.  I'll take a closer look.


Quoted text here. Click to load it

The part # I spec'd earlier is sync, but older single data rate stuff
(SDR SDRAM).  Still viable, but relatively dead technology.  I'm not
familar with Async DRAM - another name for SDR?

DDR being the next generation, the clock needs to be too regular and the
signals too well timed to bit-bang.  Yet to be proven if I can even get
SDR to work, but there are encouraging projects that show it can be
done.


Quoted text here. Click to load it

This seems like the logical course of action, since most MCUs that'd be
used with SDRAM have integrated DRAM controllers.  But this is one of
those personal quests to work the impossible. :-)


Thanks!
Richard

Re: Source for SDRAM chips
Hi,

Asynchronous DRAM is what we had before SDR. When you say "DRAM" with
no leading S, I assume you mean asynchronous DRAM. It's much simpler to
use than SDR. I haven't used DDR in a design, I kind of think of it as
a "PC component" because the micros I work with don't support it.


Site Timeline