Re: Cross-talk square-wave?

2017-03-31 Thread Noel Chiappa via cctalk
> From: Brent Hilpert > I don't have a full enough picture of the circuit and circumstances to > provide a definitive suggestion but, some principles: > ... > It's not clear C-coupling is what's going on here (the wave shape looks > pretty sharp for what I understand of

Re: Cross-talk square-wave?

2017-03-31 Thread Jon Elson via cctalk
On 03/31/2017 07:10 AM, David Bridgham via cctalk wrote: Don't trust ANYTHING! Recent Xilinx FPGAs have permanent "weak keepers" on all pins, they can not be turned off. What this is is a non-inverting receiver on the pad, that is driving back to the pad with about a 50K Ohm resistor. Plays hob

Re: Cross-talk square-wave?

2017-03-31 Thread David Bridgham via cctalk
> Don't trust ANYTHING! Recent Xilinx FPGAs have permanent "weak > keepers" on all pins, they can not be turned off. > What this is is a non-inverting receiver on the pad, that is driving > back to the pad with about a 50K Ohm resistor. > Plays hob with analog stuff like crystal oscillators.

Re: Cross-talk square-wave?

2017-03-31 Thread Mark Linimon via cctalk
On Thu, Mar 30, 2017 at 07:41:25PM -0400, allison via cctalk wrote: > *Vonada's Engineering Maxims* are a group of pithy observations about > computer engineering There's too much hard-learned truth in all that, to be funny. mcl

Re: Cross-talk square-wave?

2017-03-30 Thread Chuck Guzis via cctalk
On 03/30/2017 09:07 PM, Tony Duell via cctalk wrote: > The fundamental rule is 'You can't change the voltage across a > capacitor instantly'. There is a related one 'You can't change the > current through an inductor instantly'. It (of course) doesn't matter > if said capacitor or inductor is an

Re: Cross-talk square-wave?

2017-03-30 Thread allison via cctalk
On 03/30/2017 06:01 PM, Brent Hilpert via cctalk wrote: > On 2017-Mar-30, at 1:13 PM, Noel Chiappa via cctalk wrote: >>> From: Allison >>> FYI this is the same problem designers hit with DRAMS back 40 years ago. >> This didn't ring (pun not intended) a bell for me; can you say a bit more? >>

Re: Cross-talk square-wave?

2017-03-30 Thread Tony Duell via cctalk
On Thu, Mar 30, 2017 at 9:13 PM, Noel Chiappa via cctalk wrote: > I'm still not clear, from the discussion, how exactly that nice 'square-wave' > interference is happening - could it be capacitative crosstalk? (I'd have > thought capacitative cross-talk would be inverted -

Re: Cross-talk square-wave?

2017-03-30 Thread Jon Elson via cctalk
On 03/30/2017 10:07 PM, David Bridgham via cctalk wrote: It's not clear C-coupling is what's going on here (the wave shape looks pretty sharp for what I understand of the circuit/layout). Notably though, C-coupling would remove any DC bias, but David's screen shot indicates a DC bias on the

Re: Cross-talk square-wave?

2017-03-30 Thread David Bridgham via cctalk
> It's not clear C-coupling is what's going on here (the wave shape looks > pretty sharp for what I understand of the circuit/layout). > Notably though, C-coupling would remove any DC bias, but David's screen shot > indicates a DC bias on the line. > > Is this line currently connected to the

Re: Cross-talk square-wave?

2017-03-30 Thread Brent Hilpert via cctalk
On 2017-Mar-30, at 1:13 PM, Noel Chiappa via cctalk wrote: >> From: Allison > >> FYI this is the same problem designers hit with DRAMS back 40 years ago. > > This didn't ring (pun not intended) a bell for me; can you say a bit more? > >> From: Chuck Guzis > >> I'll offer a suggestion that if

Re: Cross-talk square-wave?

2017-03-30 Thread dwight via cctalk
7 1:59:00 PM To: General Discussion: On-Topic and Off-Topic Posts Subject: Re: Cross-talk square-wave? On 03/30/2017 01:21 PM, ben via cctalk wrote: > Well that does not solve the ring, but off loading the SD card is a > good idea, if you have the software time for a new cpu. Most o

Re: Cross-talk square-wave?

2017-03-30 Thread Chuck Guzis via cctalk
On 03/30/2017 01:21 PM, ben via cctalk wrote: > Well that does not solve the ring, but off loading the SD card is a > good idea, if you have the software time for a new cpu. Most of the > time upper managment drags thier feet, unless they want it > yesterday. Ben. Well, Noel has stated that this

Re: Cross-talk square-wave?

2017-03-30 Thread ben via cctalk
On 3/30/2017 11:22 AM, Chuck Guzis via cctalk wrote: I'll offer a suggestion that if your SD card *must* be a significant distance from its host, that you employ a small MCU at the SD card and use a more noise-immune protocol to transmit data to the host. Small MCUs today are very inexpensive.

Re: Cross-talk square-wave?

2017-03-30 Thread Noel Chiappa via cctalk
> From: Allison > FYI this is the same problem designers hit with DRAMS back 40 years ago. This didn't ring (pun not intended) a bell for me; can you say a bit more? > From: Chuck Guzis > I'll offer a suggestion that if your SD card *must* be a significant > distance from

Re: Cross-talk square-wave?

2017-03-30 Thread dwight via cctalk
t;cctalk-boun...@classiccmp.org> on behalf of W2HX via cctalk <cctalk@classiccmp.org> Sent: Wednesday, March 29, 2017 6:48:09 PM To: General Discussion: On-Topic and Off-Topic Posts Subject: RE: Cross-talk square-wave? I am still not convinced it is coupling at all. You would expect the

Re: Cross-talk square-wave?

2017-03-30 Thread Chuck Guzis via cctalk
I'll offer a suggestion that if your SD card *must* be a significant distance from its host, that you employ a small MCU at the SD card and use a more noise-immune protocol to transmit data to the host. Small MCUs today are very inexpensive. --Chuck

Re: Cross-talk square-wave?

2017-03-30 Thread Parent Allison via cctalk
rom: cctalk [mailto:cctalk-boun...@classiccmp.org] On Behalf Of Parent > Allison via cctalk > Sent: Wednesday, March 29, 2017 11:54 AM > To: Noel Chiappa; General Discussion: On-Topic and Off-Topic Posts > Subject: Re: Cross-talk square-wave? > > > On Mar 29, 2017, at 9:40 AM, Noe

RE: Cross-talk square-wave?

2017-03-29 Thread W2HX via cctalk
same effect as long as the CS line hasn't changed change in characteristic. My 2c Eugene -Original Message- From: Jon Elson [mailto:el...@pico-systems.com] Sent: Wednesday, March 29, 2017 10:55 PM To: W2HX; On-Topic and Off-Topic Posts Subject: Re: Cross-talk square-wave? On 03/29/2

Re: Cross-talk square-wave?

2017-03-29 Thread Jon Elson via cctalk
On 03/29/2017 08:48 PM, W2HX via cctalk wrote: I am still not convinced it is coupling at all. You would expect the affected line to show a signal like dV/dt , no? I just don't think you can get square waves from square waves. Yes, you can. The capacitance of typical cables is about 35 pF

Re: Cross-talk square-wave?

2017-03-29 Thread Noel Chiappa via cctalk
> From: Eugene (W2HX) > I am still not convinced it is coupling at all. ... I just don't think > you can get square waves from square waves. ... > it is even harder to believe one could successfully couple a square > wave onto such a transmission line unless the signal is

RE: Cross-talk square-wave?

2017-03-29 Thread W2HX via cctalk
iccmp.org] On Behalf Of dwight via cctalk Sent: Wednesday, March 29, 2017 8:33 PM To: Al Kossow; General Discussion: On-Topic and Off-Topic Posts Subject: Re: Cross-talk square-wave? 270K is not a transmission line load. As I recall ribbon cable is around 100-150 ohms impedance some pla

Re: Cross-talk square-wave?

2017-03-29 Thread dwight via cctalk
From: cctalk <cctalk-boun...@classiccmp.org> on behalf of Al Kossow via cctalk <cctalk@classiccmp.org> Sent: Wednesday, March 29, 2017 2:35:54 PM To: cctalk@classiccmp.org Subject: Re: Cross-talk square-wave? On 3/29/17 2:14 PM, David Bridgham via cctalk wr

Re: Cross-talk square-wave?

2017-03-29 Thread Al Kossow via cctalk
On 3/29/17 2:14 PM, David Bridgham via cctalk wrote: > And I think this picture is the smoking gun. > > http://pdp10.froghouse.org/qsic/pic_24_2.gif > > Again, the bottom trace is the CS signal in question and the upper trace > is now one of the QBUS DAL lines (after the bus transceiver and

Re: Cross-talk square-wave?

2017-03-29 Thread David Bridgham via cctalk
And I think this picture is the smoking gun. http://pdp10.froghouse.org/qsic/pic_24_2.gif Again, the bottom trace is the CS signal in question and the upper trace is now one of the QBUS DAL lines (after the bus transceiver and level converter) that's running across the ribbon cable near the CS

Re: Cross-talk square-wave?

2017-03-29 Thread David Bridgham via cctalk
> There are few things that come to mind here. The op seemed to indicate the > lines are terminated. If they are not terminated in the characteristic > impedance of the source and the transmission line, it is very unlikely he > would be seeing nice square waves at either end. The reflections

Re: Cross-talk square-wave?

2017-03-29 Thread Paul Koning via cctalk
> On Mar 29, 2017, at 1:25 PM, Paul Koning via cctalk > wrote: > > ... > SD cards are not SPI, they are a variation of MMC. Sorry about that, it turns out I was working from obsolete memories. That used to be true, isn't any longer. In any case, you're dealing with

RE: Cross-talk square-wave?

2017-03-29 Thread W2HX via cctalk
, March 29, 2017 11:54 AM To: Noel Chiappa; General Discussion: On-Topic and Off-Topic Posts Subject: Re: Cross-talk square-wave? On Mar 29, 2017, at 9:40 AM, Noel Chiappa via cctalk <cctalk@classiccmp.org> wrote: > Hi, a question about generic analog stuff. > > In the process of g

Re: Cross-talk square-wave?

2017-03-29 Thread David Bridgham via cctalk
> 270k seems like a rather strange value, it certainly can't be a termination > and it isn't a plausible pulldown either. The SD spec should explain what is > expected; I knew it at one time but forgot by now. I'll agree that 270k is a strange value. The idea is that the SD card contains an

Re: Cross-talk square-wave?

2017-03-29 Thread David Bridgham via cctalk
> 1v across 270K represents 3.7 microamps, which isn't much, particularly > at 25MHz. (I assume that you're using SPI to access the card, but the > observation still holds). Yup, I'm planning to use the SD card in SPI mode (at least for now). And this line is the CS/CD line, so it's not even

Re: Cross-talk square-wave?

2017-03-29 Thread Parent Allison via cctalk
On Mar 29, 2017, at 9:40 AM, Noel Chiappa via cctalk wrote: > Hi, a question about generic analog stuff. > > In the process of getting SD cards to work, Dave is seeing square-wave noise > on a line. (1V of square wave, with pulses about 400ns long, running at > 375kHz.)

RE: Cross-talk square-wave?

2017-03-29 Thread Noel Chiappa via cctalk
I should mention that this is a pre-prototype; the final thing won't have a cable at all; so this isn't a fundamental issue with the design (if it is cross-talk). And the SD card isn't even plugged in when we see this - if it is cross-talk, it has to be some other signal carried in the cable.

Re: Cross-talk square-wave?

2017-03-29 Thread Paul Koning via cctalk
> On Mar 29, 2017, at 1:17 PM, Chuck Guzis via cctalk > wrote: > > On 03/29/2017 07:08 AM, Noel Chiappa via cctalk wrote: >>> From: Dwight Kelvey >> >>> Is there any load resistance at the end of the line? >> >> Yes, 270K to ground (i.e. pretty large). How does that

Re: Cross-talk square-wave?

2017-03-29 Thread Chuck Guzis via cctalk
On 03/29/2017 07:08 AM, Noel Chiappa via cctalk wrote: >> From: Dwight Kelvey > >> Is there any load resistance at the end of the line? > > Yes, 270K to ground (i.e. pretty large). How does that have an effect > on whether cross-talk can create a square wave? Sorry, I'm not > understanding. 1v

Re: Cross-talk square-wave?

2017-03-29 Thread Noel Chiappa via cctalk
> From: Dwight Kelvey > Is there any load resistance at the end of the line? Yes, 270K to ground (i.e. pretty large). How does that have an effect on whether cross-talk can create a square wave? Sorry, I'm not understanding. Noel

Re: Cross-talk square-wave?

2017-03-29 Thread dwight via cctalk
mp.org Cc: j...@mercury.lcs.mit.edu Subject: Cross-talk square-wave? Hi, a question about generic analog stuff. In the process of getting SD cards to work, Dave is seeing square-wave noise on a line. (1V of square wave, with pulses about 400ns long, running at 375kHz.) The line runs through a flat cable of modest l

Cross-talk square-wave?

2017-03-29 Thread Noel Chiappa via cctalk
Hi, a question about generic analog stuff. In the process of getting SD cards to work, Dave is seeing square-wave noise on a line. (1V of square wave, with pulses about 400ns long, running at 375kHz.) The line runs through a flat cable of modest length, along with other signal-carrying lines.