On Nov 13, 3:20 pm, sendt...@gmail.com wrote:
> On Nov 6, 3:13 pm, sendt...@gmail.com wrote:
>
>
>
> > On Oct 25, 6:43 pm, sendt...@gmail.com wrote:
>
> > > On Oct 16, 5:48 pm, CBFalconer <cbfalco...@yahoo.com> wrote:
>
> > > > sendt...@gmail.com wrote:
>
> > > > > I'm trying to design a test setup to do radiation experiments on
> > > > > SDR DRAM for my thesis. The DRAM needs to be isolated from our
> > > > > control unit b/c I'm worried about contaminating our results by
> > > > > having our control circuitry in there too - b/c then how do we
> > > > > know if it's the DRAM or "something" else that fails.
>
> > > > > So my question is, what's the longest length I can run a ribbon
> > > > > cable (or other type of connection) and not having issues? Can
> > > > > I bring the clock down? We are using 20-24 inches of cabling. We
> > > > > decided maybe to use CAT6 cable?
>
> > > > You can get a rough idea by the propagation time.  2 feet of cable
> > > > will have a one-way propagation time in the order of 2 nanosecs,
> > > > and a characteristic impedance in the order of 100 ohms.  So
> > > > ringing will be in the order of 250 MHz.  The cures are proper
> > > > matching and timing.
>
> > > > --
> > > >  Chuck F (cbfalconer at maineline dot net)
> > > >    Available for consulting/temporary embedded and systems.
> > > >    <http://cbfalconer.home.att.net>
>
> > > > --
> > > > Posted via a free Usenet account fromhttp://www.teranews.com
>
> > > That seems reasonable. I'm using a 20 or 50Mhz clock but I can
> > > certainly slow it down or speed it up fairly easily. The cabling is
> > > made with twisted pair although they're not perfectly the same length.
> > > There's also a short length of it (to be reduced) that's using ribbon
> > > cable.
>
> > > I guess I'll know soon enough if it works or not since we pressed
> > > ahead with building a test fixture. I'll let everyone know how it
> > > works out...
>
> > > Thanks,
>
> > > Eric- Hide quoted text -
>
> > > - Show quoted text -
>
> > Well we've been playing with the test fixture for a while now. It
> > doesn't appear to be working. Not sure if it's due to skew although
> > we're compensating that with a PLL. We're also getting some voltage
> > spikes.
>
> > We're going to reduce the wire lengths and see if that helps. If so,
> > then we'll need to redesign our test. If not, I don't know what to do.- Hide quoted text -
>
> > - Show quoted text -
>
> Actually we manage to get it working. There's still some jitter and
> ringing but we hope to be able to clean that up with some tweaking.
> Thanks for the help.
> So if anyone ever needs to run DRAM over 20 inches of wire, use
> twisted pair and run it at a 10 Mhz clock... we have had some success
> over a 50Mhz clock...

Without termination we got it to run perfectly (passed some basic
memory scans) on 4 inches of twisted pair at 66.66667 Mhz. It fails
somewhere between 66.67Mhz and 75Mhz but it wasn't important to find
exactly when it failed.

On the longer cable, ~24 inches, it passes the memory scan at 20 Mhz
without any type of  termination.

On Nov 6, 3:13 pm, sendt...@gmail.com wrote:
> On Oct 25, 6:43 pm, sendt...@gmail.com wrote:
>
>
>
>
>
> > On Oct 16, 5:48 pm, CBFalconer <cbfalco...@yahoo.com> wrote:
>
> > > sendt...@gmail.com wrote:
>
> > > > I'm trying to design a test setup to do radiation experiments on
> > > > SDR DRAM for my thesis. The DRAM needs to be isolated from our
> > > > control unit b/c I'm worried about contaminating our results by
> > > > having our control circuitry in there too - b/c then how do we
> > > > know if it's the DRAM or "something" else that fails.
>
> > > > So my question is, what's the longest length I can run a ribbon
> > > > cable (or other type of connection) and not having issues? Can
> > > > I bring the clock down? We are using 20-24 inches of cabling. We
> > > > decided maybe to use CAT6 cable?
>
> > > You can get a rough idea by the propagation time.  2 feet of cable
> > > will have a one-way propagation time in the order of 2 nanosecs,
> > > and a characteristic impedance in the order of 100 ohms.  So
> > > ringing will be in the order of 250 MHz.  The cures are proper
> > > matching and timing.
>
> > > --
> > >  Chuck F (cbfalconer at maineline dot net)
> > >    Available for consulting/temporary embedded and systems.
> > >    <http://cbfalconer.home.att.net>
>
> > > --
> > > Posted via a free Usenet account fromhttp://www.teranews.com
>
> > That seems reasonable. I'm using a 20 or 50Mhz clock but I can
> > certainly slow it down or speed it up fairly easily. The cabling is
> > made with twisted pair although they're not perfectly the same length.
> > There's also a short length of it (to be reduced) that's using ribbon
> > cable.
>
> > I guess I'll know soon enough if it works or not since we pressed
> > ahead with building a test fixture. I'll let everyone know how it
> > works out...
>
> > Thanks,
>
> > Eric- Hide quoted text -
>
> > - Show quoted text -
>
> Well we've been playing with the test fixture for a while now. It
> doesn't appear to be working. Not sure if it's due to skew although
> we're compensating that with a PLL. We're also getting some voltage
> spikes.
>
> We're going to reduce the wire lengths and see if that helps. If so,
> then we'll need to redesign our test. If not, I don't know what to do.- Hide quoted text -
>
> - Show quoted text -

Actually we manage to get it working. There's still some jitter and
ringing but we hope to be able to clean that up with some tweaking.
Thanks for the help.
So if anyone ever needs to run DRAM over 20 inches of wire, use
twisted pair and run it at a 10 Mhz clock... we have had some success
over a 50Mhz clock...

On Oct 25, 6:43 pm, sendt...@gmail.com wrote:
> On Oct 16, 5:48 pm, CBFalconer <cbfalco...@yahoo.com> wrote:
>
>
>
>
>
> > sendt...@gmail.com wrote:
>
> > > I'm trying to design a test setup to do radiation experiments on
> > > SDR DRAM for my thesis. The DRAM needs to be isolated from our
> > > control unit b/c I'm worried about contaminating our results by
> > > having our control circuitry in there too - b/c then how do we
> > > know if it's the DRAM or "something" else that fails.
>
> > > So my question is, what's the longest length I can run a ribbon
> > > cable (or other type of connection) and not having issues? Can
> > > I bring the clock down? We are using 20-24 inches of cabling. We
> > > decided maybe to use CAT6 cable?
>
> > You can get a rough idea by the propagation time.  2 feet of cable
> > will have a one-way propagation time in the order of 2 nanosecs,
> > and a characteristic impedance in the order of 100 ohms.  So
> > ringing will be in the order of 250 MHz.  The cures are proper
> > matching and timing.
>
> > --
> >  Chuck F (cbfalconer at maineline dot net)
> >    Available for consulting/temporary embedded and systems.
> >    <http://cbfalconer.home.att.net>
>
> > --
> > Posted via a free Usenet account fromhttp://www.teranews.com
>
> That seems reasonable. I'm using a 20 or 50Mhz clock but I can
> certainly slow it down or speed it up fairly easily. The cabling is
> made with twisted pair although they're not perfectly the same length.
> There's also a short length of it (to be reduced) that's using ribbon
> cable.
>
> I guess I'll know soon enough if it works or not since we pressed
> ahead with building a test fixture. I'll let everyone know how it
> works out...
>
> Thanks,
>
> Eric- Hide quoted text -
>
> - Show quoted text -

Well we've been playing with the test fixture for a while now. It
doesn't appear to be working. Not sure if it's due to skew although
we're compensating that with a PLL. We're also getting some voltage
spikes.

We're going to reduce the wire lengths and see if that helps. If so,
then we'll need to redesign our test. If not, I don't know what to do.

On Oct 16, 5:48 pm, CBFalconer <cbfalco...@yahoo.com> wrote:
> sendt...@gmail.com wrote:
>
> > I'm trying to design a test setup to do radiation experiments on
> > SDR DRAM for my thesis. The DRAM needs to be isolated from our
> > control unit b/c I'm worried about contaminating our results by
> > having our control circuitry in there too - b/c then how do we
> > know if it's the DRAM or "something" else that fails.
>
> > So my question is, what's the longest length I can run a ribbon
> > cable (or other type of connection) and not having issues? Can
> > I bring the clock down? We are using 20-24 inches of cabling. We
> > decided maybe to use CAT6 cable?
>
> You can get a rough idea by the propagation time.  2 feet of cable
> will have a one-way propagation time in the order of 2 nanosecs,
> and a characteristic impedance in the order of 100 ohms.  So
> ringing will be in the order of 250 MHz.  The cures are proper
> matching and timing.
>
> --
>  Chuck F (cbfalconer at maineline dot net)
>    Available for consulting/temporary embedded and systems.
>    <http://cbfalconer.home.att.net>
>
> --
> Posted via a free Usenet account fromhttp://www.teranews.com

That seems reasonable. I'm using a 20 or 50Mhz clock but I can
certainly slow it down or speed it up fairly easily. The cabling is
made with twisted pair although they're not perfectly the same length.
There's also a short length of it (to be reduced) that's using ribbon
cable.

I guess I'll know soon enough if it works or not since we pressed
ahead with building a test fixture. I'll let everyone know how it
works out...

Thanks,

Eric

>  > The DRAM needs to be isolated from our control unit
>
> What kind of "isolation"?
>

When I mean isolated, I mean, "away from". The DRAM must be 19 inches
away from the irradiation source.

>
> Ultimately, you never do.  That's why people do stability checks, a.k.a.
> calibration runs, where they measure the effect of the experimental
> environment on the measurement devices themselves.
>
> > So my question is, what's the longest length I can run a ribbon cable
> > (or other type of connection) and not having issues?
>
> I'll second the guess already voiced here before: zero.  SDRAM signals
> aren't designed to travel on pretty much anything else than short(!),
> scrupulously designed traces on multi-layer PCBs.

That's what I originally thought too, but people I asked (who don't
necessarily have experience in the subject) said it seems reasonable
to assume it's okay. We ended up using CAT5e cable for the cabling...

On Oct 16, 6:27 pm, Jim Stewart <jstew...@jkmicro.com> wrote:
> sendt...@gmail.com wrote:
> > I'm trying to design a test setup to do radiation experiments on SDR
> > DRAM
> > for my thesis. The DRAM needs to be isolated from our control unit b/c
> > I'm
> > worried about contaminating our results by having our control
> > circuitry
> > in there too - b/c then how do we know if it's the DRAM or
> > "something"
> > else that fails.
>
> > So my question is, what's the longest length I can run a ribbon cable
> > (or other type of connection) and not having issues? Can I bring the
> > clock down? We are using 20-24 inches of cabling. We decided maybe to
> > use CAT6 cable?
>
> A stupid question.
>
> Are you exposing the SDRAM to radiation
> or are you measuring EMI from the SDRAM?

I'm exposing it to radiation. And I knew what you meant by "A stupid
question" when I read it, but thanks for clarifying anyway.

> What was your clock rate again?
>

Well I'm willing to provide ANY clock rate. I'm trying 20 Mhz because
that seemed like a reasonable clock speed to work with. The data sheet
didn't specify a minimum clock speed but I would assume it would have
to be at least fast enough to provide a refresh rate (~100kHz).

sendthis@gmail.com wrote:

> I'm trying to design a test setup to do radiation experiments on SDR 
> DRAM for my thesis.

Forgive me for being a physicist but: what kind of radiation would that be?

 > The DRAM needs to be isolated from our control unit

What kind of "isolation"?

> - b/c then how do we know if it's the DRAM or
> "something" else that fails.

Ultimately, you never do.  That's why people do stability checks, a.k.a. 
calibration runs, where they measure the effect of the experimental 
environment on the measurement devices themselves.

> So my question is, what's the longest length I can run a ribbon cable
> (or other type of connection) and not having issues? 

I'll second the guess already voiced here before: zero.  SDRAM signals 
aren't designed to travel on pretty much anything else than short(!), 
scrupulously designed traces on multi-layer PCBs.

Tom Lucas wrote:
> "Jim Stewart" <jstewart@jkmicro.com> wrote in message 
> news:D9OdnUGssp1Zp4janZ2dnUVZ_r_inZ2d@omsoft.com...
>> sendthis@gmail.com wrote:
>>> I'm trying to design a test setup to do radiation experiments on SDR
>>> DRAM
>>> for my thesis. The DRAM needs to be isolated from our control unit 
>>> b/c
>>> I'm
>>> worried about contaminating our results by having our control
>>> circuitry
>>> in there too - b/c then how do we know if it's the DRAM or
>>> "something"
>>> else that fails.
>>>
>>> So my question is, what's the longest length I can run a ribbon cable
>>> (or other type of connection) and not having issues? Can I bring the
>>> clock down? We are using 20-24 inches of cabling. We decided maybe to
>>> use CAT6 cable?
>> A stupid question.
> 
> That's a bit harsh, although the poor chap seems unable to spell 
> "because".

My apologies to the original poster and
the group.  My meaning was "I have a
stupid question".

>> Are you exposing the SDRAM to radiation
>> or are you measuring EMI from the SDRAM?
> 
> Either way the OP could probably get reasonable results by wrapping his 
> controller up in aluminium foil or, more professionally, a metal 
> enclosure with proper braided earthing. However, I believe they 
> mentioned that they were expecting the device to fail so presumably they 
> are testing for EMI succeptibility. 
> 
> 

"Jim Stewart" <jstewart@jkmicro.com> wrote in message 
news:D9OdnUGssp1Zp4janZ2dnUVZ_r_inZ2d@omsoft.com...
> sendthis@gmail.com wrote:
>> I'm trying to design a test setup to do radiation experiments on SDR
>> DRAM
>> for my thesis. The DRAM needs to be isolated from our control unit 
>> b/c
>> I'm
>> worried about contaminating our results by having our control
>> circuitry
>> in there too - b/c then how do we know if it's the DRAM or
>> "something"
>> else that fails.
>>
>> So my question is, what's the longest length I can run a ribbon cable
>> (or other type of connection) and not having issues? Can I bring the
>> clock down? We are using 20-24 inches of cabling. We decided maybe to
>> use CAT6 cable?
>
> A stupid question.

That's a bit harsh, although the poor chap seems unable to spell 
"because".

> Are you exposing the SDRAM to radiation
> or are you measuring EMI from the SDRAM?

Either way the OP could probably get reasonable results by wrapping his 
controller up in aluminium foil or, more professionally, a metal 
enclosure with proper braided earthing. However, I believe they 
mentioned that they were expecting the device to fail so presumably they 
are testing for EMI succeptibility.