Old analogue scopes beat new digital scopes, for bit-bashed digital outputs - Page 1
Forum section: electronics / testgear

author: tggzzz
author_rank: Super Contributor
timestamp: May 28, 2017, 11:23:08 pm
content: That statement should provoke the immune responseThe standard statement seen all too often on this forum is that an entry-level Rigol scope is better than an old analogue scope. But is that really true for a common basic use-case: a beginner looking at bit-bashed outputs from a microprocessor?Test setup:alow-endDevKitfor amodern microprocessor, cost £12 from Digikey or Farnella 1.5GHz Z0 probe connected across one processor I/O pin; that is sufficiently good that it won't affect the measurementsbit-bashed single bit output in softwareRigol DS1052E: borrowed, cost £275Tektronix 2465 scope: cost £84 and working, but I prophylactically replaced the mains X and Y filter capacitorsThe first point to note is that the 80:20 transition times of the output is 1ns (90:10 is 1.8ns). Using the BW=0.35/tr rule-of-thumb, that implies a 350MHz scope is required to measure the risetime. Hence a 50MHz scope is completely inadequate when checking signal integrity of a modern microprocessor's outputs. There is absolutely no doubt about that, and no surprises either.But if you (falsely) regard that as “esoteric”, what about bit-bashed outputsusing only the hardware inside the processor? It will be seen that low-end digitising scopes can be inadequate and/or misleading compared with cheaper old analogue scopes.Before replying, please note my repeated statements elsewhere in the forum:choose the right tool for the job. Occasionally a digitising scope is necessary, occasionally an old analogue scope is necessary,frequently either are sufficient.And yes, Idoknow the reasons for the displays shown, and (where possible) which sequence of 5 buttons to press to get the expected traces. But would a beginner know? If not, what would their reaction be? for the curious, that low end XMOS microprocessor and DevKit can drive at least 4 I/O ports as shown in the tests, withguaranteedtimings down to 4ns resolution, whilesimultaneouslycommunicating with a host PC over a USB link. Not bad, and IMNSHO makes Arduino-class machines look anaemic.

author: tggzzz
author_rank: Super Contributor
timestamp: May 28, 2017, 11:25:38 pm
content: In this test the program sits in a tight loop outputting a constant pattern (0x005555ff) using an I/O port's SERDES output running as fast as possible.While the old Tek 2465 displays a sensible waveform, the new Rigol is clearly struggling; it looks like the logic signals are invalid.I'm not going to explain the details of the code, other than to note that the "outPort <:0x005555ff" outputs the pattern after any previous output has completed. FFI see theintroduction to xC.Code:clock clk0 = XS1_CLKBLK_2;buffered out port:32 outPort = XS1_PORT_1C;void processes() {configure_clock_rate(clk0, 250, 1);configure_out_port(outPort, clk0, 1);start_clock(clk0);while (1) {outPort <:0x005555ff;}}

author: tggzzz
author_rank: Super Contributor
timestamp: May 28, 2017, 11:32:02 pm
content: This is a simple 10kHz waveform output.The old analogue scope display is clear and simple - and correct.But the (single shot) digitising scope display is woefully incorrect. When not in single shot mode, the trace twinkles like a demented Christmas decoration!(EDIT added for clarification. That is avery common waveformin hard realtime systems, when you are blipping a bit to see how fast/slow a loop is occurring, or the latency between two events, typically a stimulus and a response)Code:clock clk0 = XS1_CLKBLK_2;out port outPort = XS1_PORT_1C;void processes() {timer tmr;uint32_t t;configure_clock_rate(clk0, 250, 1);configure_out_port(outPort, clk0, 1);start_clock(clk0);while (1) {outPort <: 1;outPort <: 1;outPort <: 1;outPort <: 1;outPort <: 0;tmr :> t;t = t + 10000; // 10ns clock cyclesselect {case tmr when timerafter(t) :> void:// wait for precisely 10000 clock cyclesbreak;}}}

author: P90
author_rank: Frequent Contributor
timestamp: May 28, 2017, 11:45:42 pm
content: coming soon to a theater near you...

author: ataradov
author_rank: Super Contributor
timestamp: May 29, 2017, 12:07:55 am
content: So if all you do is observe repeating signals, then sure go ans stare at your analogue scope. How about outputting incrementing counter in one of the digits and meaningfully observing that? We are talking about digital signals after all.Also, does your Rigol has 20 MHz BW limit enabled by any chance?

author: tggzzz
author_rank: Super Contributor
timestamp: May 29, 2017, 12:29:06 am
content: Quote from: ataradov on May 29, 2017, 12:07:55 amTraditionally, and especially for PRBS sequences, that is done with an eye diagram, for both analogue and high-end digitising scopes. Eye diagrams with low-end digitising scopes can, depending on the digitising scope, be another source of bafflement. I may get around to showing an example of that (in an Agilent scope) scope next week. I might even throw together a PRBS sequence tomorrow, if Real Life doesn't intervene.Beyond that, if you know you are observing valid digital signals, then it is usually more appropriate to examine them with digital instruments such as a logic analyser or printf statements.Please look at the paragraph in the first post starting "Before replying".QuoteNo.

author: xrunner
author_rank: Super Contributor
timestamp: May 29, 2017, 12:32:15 am
content: Quote from: tggzzz on May 28, 2017, 11:23:08 pmIndeed, the statement we've all read around here "an entry-level Rigol scope is better than an old analogue scope" is too simplistic, as you've very clearly demonstrated. The hobby is clearly too varied and complex for people to utter such a statement. But that being said, I doubt many new young hobbyists would go for the old analog scope even if you tried to convince them with your data, as the bling of colors, screen shots, USB ports, and LCD displays would be too attractive. But there's always hope a few would listen.

author: ataradov
author_rank: Super Contributor
timestamp: May 29, 2017, 12:32:32 am
content: Quote from: tggzzz on May 29, 2017, 12:29:06 amTraditionally it is done that way because of crappy outdated equipment. With modern equipment you can capture a lot of real-time data, and do all sorts of analysis on it.But yeah, I'm not going to waste much more of my time on this.

author: tggzzz
author_rank: Super Contributor
timestamp: May 29, 2017, 12:35:24 am
content: Quote from: ataradov on May 29, 2017, 12:32:32 amDon't ignore the cost implications of your statement. For the past 40 years the rule of thumb has been that the scope you wantandcan reasonably expect to have costs about a year's salary.

author: ataradov
author_rank: Super Contributor
timestamp: May 29, 2017, 12:41:50 am
content: Quote from: tggzzz on May 29, 2017, 12:35:24 amWhen debugging digital signals, I can reasonably live with bandwidth limitations. In general, just get the best scope you can, and factor its limitations into observed results.I routinely use advanced triggering modes, not available on analogue scopes. I have no doubts that there are techniques to works around that as well, but I'd rather use equipment that directly lets me do what I want to do.

author: KE5FX
author_rank: Super Contributor
timestamp: May 29, 2017, 12:47:45 am
content: Low-grade DSO with (deliberately) incorrect operating procedure beaten by older high-performance analog model that is somewhat harder to misconfigure.Ric Romero has film at 11!

author: tautech
author_rank: Super Contributor
timestamp: May 29, 2017, 01:05:55 am
content: Blah, blah, blah.Any mugginsthat can readcan see the limitations of their scope AND the specified transition times of devices there are trying to measure.Bashing blindly into measurements without these simple facts being observed and how they might confuse the user is demonstrated nearly everyday on this forum.Old news...........over and out.

author: snoopy
author_rank: Frequent Contributor
timestamp: May 29, 2017, 01:12:48 am
content: Quote from: tggzzz on May 28, 2017, 11:25:38 pmWhy is the Rigol scope stopped when the Analog scope can't be stopped ? Try running the Rigol scope with repetitive triggering.Also this Rigol scope is fairly old with shallow record depth and no Peak detect. Try a later scope such as the 1054Z etc.You should compare apples with apples !! Also for digital signals you should preferably use linear interpolation rather than sinX/X interpolation.

author: nidlaX
author_rank: Frequent Contributor
timestamp: May 29, 2017, 01:13:57 am
content: Also, who the fuck pays 275 pounds for a 1052E??

author: P90
author_rank: Frequent Contributor
timestamp: May 29, 2017, 01:15:17 am
content: Quote from: nidlaX on May 29, 2017, 01:13:57 amobviously someone in the UK...LOL

author: 3db
author_rank: Frequent Contributor
timestamp: May 29, 2017, 01:21:56 am
content: @tggzzzI loved your description " the trace twinkles like a demented Christmas decoration!"3DB

author: mtdoc
author_rank: Super Contributor
timestamp: May 29, 2017, 01:54:10 am
content: Let's see how many "immune responses" are triggered and replies made without reading the qualifications stated in the OP.

author: Electro Detective
author_rank: Super Contributor
timestamp: May 29, 2017, 03:00:22 am
content: Megahertz considerations aside for a nanosecond,can the audio frequency community be guaranteed accurate, precise, audiophool transparency(?) with cheap DSOs from 6hz up to 30khz? (100khz would be nicer, lol)Or must they still rely on analogue scopes to check/view their hi-fi, recording gear and synthesizer performance etci.e. can they TRUST that the DSO is truly WYSIWYG from 6hz up to 30khz (this includes pulse, square, triangle, weird, not just simple sine waves) without resorting to buying (or keeping) an old school CRO to get the job done PROPERLY?

author: ataradov
author_rank: Super Contributor
timestamp: May 29, 2017, 03:04:06 am
content: Audiophools don't need any measurements, they can hear stuff. Because when you measure, you get objective numbers, and that just kills the buzz from paying $1000 for a power cable

author: Electro Detective
author_rank: Super Contributor
timestamp: May 29, 2017, 03:17:50 am
content: Quote from: ataradov on May 29, 2017, 03:04:06 amGood point, my comment above should have included DSO performance powered WITH $1000 IEC power cableSolid gold RCA to BNC adapters freshly dipped in DEOXIT,and let's not forget the oxygen free audio cables in vacuum tight blister packaging, for one shot use only,otherwise the calibrated performance will degrade with time,due to the aged audio electron cadavers blocking the narrow frequency response time domain sonic corridor.Did I miss anything?

author: rstofer
author_rank: Super Contributor
timestamp: May 29, 2017, 03:23:38 am
content: Comparing a 50 MHz Rigol against a 300 MHz Tektronix doesn't prove a lot. Of course the Tek has more bandwidth.I didn't toss my 350 MHz Tek 485 just because I bought the 100 MHz Rigol DS1054X. Different tools for different jobs.I see no point in comparing the scopes. And, yes, I can get a 350 MHz 485 for a couple of hundred dollars. But it still won't decode SPI or provide measurements or do single shot or FFT or any of the other things a modern DSO can do. It does have the bandwidth advantage.Pretty meaningless comparison...

author: Paul Moir
author_rank: Frequent Contributor
timestamp: May 29, 2017, 04:47:25 am
content: I disagree completely, and I'll give you an example of why. Just a few days ago, I was unexpectedly debugging a 16 bit, bit banged SPI transfer. Since my DSO is in the mail (or possibly hasn't been manufactured yet) I had to use my analog CRO, with the intensity set way up, the lights turned out and a bunch of shots with my cell phone camera hoping for a lucky strike.If you look at the trace, you'll see the upper is the SCLK and the bottom is the data. Due to the bit banging, it hangs a bit between bytes. However the data is completely wrong: the first few bits should be 0.After too much time I found the problem. My 3 almost 4 year old nephew had previously pressed practically every button on the 'scope. While I had reset most, I neglected the 2nd channel invert button. Therefore any DSO is superior to an old analog CRO because the invert channel 2 button doesn't exist.

author: ataradov
author_rank: Super Contributor
timestamp: May 29, 2017, 04:49:41 am
content: Quote from: Paul Moir on May 29, 2017, 04:47:25 amThat's how shamans traditionally did it

author: Fungus
author_rank: Super Contributor
timestamp: May 29, 2017, 06:23:34 am
content: Let's see if I've got this straight:We're looking at a 150MHz signal on a 50MHz DSO and a 300MHz Analog 'scope and concluding that Analog 'scopes are "better"?QuoteNo it isn't. It's a program that generates 10,000 very narrow pulses per second.Code:outPort <: 1;outPort <: 1;outPort <: 1;outPort <: 1;outPort <: 0;Is there a reason for having 4 ones and 99996 zeros?(I mean apart from when you manually tuned the program to look bad on the 50MHz DSO?)

author: tggzzz
author_rank: Super Contributor
timestamp: May 29, 2017, 06:31:45 am
content: Quote from: snoopy on May 29, 2017, 01:12:48 amIf you think about it, that makes no difference.QuoteAs I said, I know how to get the expected trace: change from "normal" to "peak detect"; IMNSHO peak detectshouldbe the normal setting!QuoteIf you read the first post, you will see I am doing exactly what many posts on this forum recommend.Thatis the point.BTW, sin/x wasoff- and is irrelevant anyway.

author: tggzzz
author_rank: Super Contributor
timestamp: May 29, 2017, 06:36:49 am
content: Quote from: rstofer on May 29, 2017, 03:23:38 amOh, I agree with all of that - but that wasn't the point of the post!The point was to highlight the consequences of typical statements made in this forum.

author: tggzzz
author_rank: Super Contributor
timestamp: May 29, 2017, 06:37:55 am
content: Quote from: nidlaX on May 29, 2017, 01:13:57 amThe usual advice in this forum is "buy new and get the guarantee"; so I just lifted the price from the Rigol website.

author: tggzzz
author_rank: Super Contributor
timestamp: May 29, 2017, 06:41:33 am
content: Quote from: Paul Moir on May 29, 2017, 04:47:25 amOut of curiosity, what was the bit rate? I might try to duplicate that on an analogue storage scope, for purely masochistic fun, of course.

author: tggzzz
author_rank: Super Contributor
timestamp: May 29, 2017, 06:59:36 am
content: Quote from: Fungus on May 29, 2017, 06:23:34 amNot quiteLook at the first post, and seewhyI've shown the two sets of results.QuoteThatisa very simple waveform. It is also avery common waveformwhen you are blipping a bit to seehow fast/slow a loop is occurringlatency between two events, typically a stimulus and a responseHence I observe such waveforms most days when I am debugging and performance testing hard realtime systems.QuoteI was wondering if someone would ask that! The results would be exactly the same if the program wasconfigure_clock_rate(clk0, 250, 4);...outPort <: 1;outPort <: 0;...And, as I said above, such waveforms are probably the most common ones I generate and observe. I should have made that explicit in the first post; mea culpa.

author: tggzzz
author_rank: Super Contributor
timestamp: May 29, 2017, 07:06:20 am
content: Quote from: mtdoc on May 29, 2017, 01:54:10 amToo many, but that was anticipatedSome people will also jump on obscure points whether or not they are correct and/or support their contention and/or whether or not they are relevant to the reason for the first posts.

author: Fungus
author_rank: Super Contributor
timestamp: May 29, 2017, 07:22:47 am
content: Quote from: tggzzz on May 29, 2017, 06:59:36 amI already knowwhyyou've done it.QuoteYou're doing it wrong.Clue: Toggle the pin instead of blipping it then you can use the DSO's pulse width measurement to get the elapsed time instead of trying to count fractions of squares on a a green screen.(You do have pulse width measurement on the Analog 'scope, right?)You'll also save three clock cycles.

author: Fungus
author_rank: Super Contributor
timestamp: May 29, 2017, 07:27:56 am
content: Quote from: tggzzz on May 29, 2017, 06:59:36 amMath. It works, bitches!But the reason you can't dosixone was...?

author: nctnico
author_rank: Super Contributor
timestamp: May 29, 2017, 07:40:51 am
content: Quote from: tggzzz on May 28, 2017, 11:25:38 pmAll you have proven here is that a 50MHz scope isn't up to the job (assuming it is setup properly). This is a GDS2204E 200MHz DSO decoding a 125MHz SPI bus:

author: nctnico
author_rank: Super Contributor
timestamp: May 29, 2017, 07:51:56 am
content: Quote from: nctnico on May 29, 2017, 07:40:51 amBTW that Rigol isn't new but very old. Turning on peak detect will help a lot to see more.If you are trying to prove analog scopes work easier then I think you are wrong. Sometimes training wheels cause more problems than they solve.

author: tggzzz
author_rank: Super Contributor
timestamp: May 29, 2017, 07:55:02 am
content: Quote from: Fungus on May 29, 2017, 07:22:47 amTime accuracy is indeed one of the significant advantages of digital scopes; no surprises there. But not the point being made.Usefully, with XMOS processors and xC it is trivial to have a specified pulsewidth with almost zero software impact. There are language and hardware constructs stating "change the output to X at clock tick Y". But not many people are using XMOS processors.

author: tggzzz
author_rank: Super Contributor
timestamp: May 29, 2017, 07:57:34 am
content: Quote from: nctnico on May 29, 2017, 07:40:51 amOf course; no surprises there.But read the first post to see that I deliberately chose the tests to show the consequences of typical advice on this forum.

author: tggzzz
author_rank: Super Contributor
timestamp: May 29, 2017, 08:00:43 am
content: Quote from: nctnico on May 29, 2017, 07:51:56 amOf course. As I said, I know which 5 buttons to press to change from the "normal" (that's what is it called) setting to "peak detect". But beginners might not even notice the choice exists.(I've skipped over the point that not all digitising scopes have peak detect)QuoteThat point can legitimately be argued in either direction, but simplicity is usually a virtue.

author: Fungus
author_rank: Super Contributor
timestamp: May 29, 2017, 08:15:41 am
content: Quote from: tggzzz on May 29, 2017, 07:55:02 amSo, ummmm ... your argument is: It wouldn't cost you anything to make it wide enough to see on your DSO.Is that right?

author: Fungus
author_rank: Super Contributor
timestamp: May 29, 2017, 08:17:30 am
content: Quote from: tggzzz on May 29, 2017, 08:00:43 amHammers are simple! (but not much use for driving screws)

author: tggzzz
author_rank: Super Contributor
timestamp: May 29, 2017, 08:34:32 am
content: Quote from: Fungus on May 29, 2017, 08:15:41 amFor people wise enough to use XMOS processors, it wouldn't cost anything. But this thread is about unthinking advice given to beginners; how many beginners use XMOS processors?

author: tggzzz
author_rank: Super Contributor
timestamp: May 29, 2017, 08:35:44 am
content: Quote from: Fungus on May 29, 2017, 08:17:30 amI've said that too many times. (I've also noted that professional sometimes hammer screws into wood, except for the last turn).But let's keep away from homilies; they obscure as much as they reveal.

author: Fungus
author_rank: Super Contributor
timestamp: May 29, 2017, 08:43:38 am
content: Quote from: tggzzz on May 29, 2017, 08:35:44 amThat doesn't mean that amateurs can.Hammering in a screw takesyearsof experience.

author: nctnico
author_rank: Super Contributor
timestamp: May 29, 2017, 08:46:16 am
content: Quote from: tggzzz on May 29, 2017, 08:00:43 amThen they'll learn an important lesson: RTFM!The way you are reasoning everyone should crawl because it takes effort to learn to walk, ride a bike and/or how to drive a car.

author: tggzzz
author_rank: Super Contributor
timestamp: May 29, 2017, 08:54:05 am
content: Quote from: nctnico on May 29, 2017, 08:46:16 amRTFM is necessary but insufficient; it should be R&UTFM. The "& Understand" is a chicken-and-egg problem with beginners given unthinking overly dogmatic advice.Everybody does learn to crawl before they learn to walk - so your statement adds nothing to the conversation.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: May 29, 2017, 08:56:46 am
content: QuoteYes, absolutely.The reason the beginner is looking at the output is to see if their code is doing the right thing. They need to capture the output. zoom in, make timing measurements and tweak code until it's right.To suggest that an analogue scope is better for this is just ridiculous.There are probably some areas where an analogue scope beats an old or lowest-end digital scope, (but this isn't one of them).Any digital scope with reasonable memory and intensity display beats an analogue scope in pretty much all respects.

author: ebastler
author_rank: Super Contributor
timestamp: May 29, 2017, 09:15:36 am
content: Quote from: tggzzz on May 28, 2017, 11:23:08 pmI assume there was some Freudian slip at work when you typed the "bit-bashing" title?Well; nothing wrong with some bit-banging, scope-bashing fun on a slow day...

author: Fungus
author_rank: Super Contributor
timestamp: May 29, 2017, 09:34:59 am
content: Quote from: tggzzz on May 29, 2017, 08:34:32 amNo it isn't, it's a troll.

author: Jwalling
author_rank: Unknown
timestamp: May 29, 2017, 09:53:31 am
content: Quote from: Fungus on May 29, 2017, 09:34:59 amAnd, as always when this subject comes up, successful!

author: tggzzz
author_rank: Super Contributor
timestamp: May 29, 2017, 09:56:08 am
content: Quote from: ebastler on May 29, 2017, 09:15:36 amPossiblyBut I've heard both terms used.Strictly speaking my point isn't scope bashing, since the scopes are performing to specification and as expected. Know your tools, understand their limitations. And make explicit the limitations of advice given to beginners.

author: tggzzz
author_rank: Super Contributor
timestamp: May 29, 2017, 09:57:52 am
content: Quote from: Jwalling on May 29, 2017, 09:53:31 amIt is a shame people ignore the multiple explicit caveats in the first post.

author: Fungus
author_rank: Super Contributor
timestamp: May 29, 2017, 10:04:50 am
content: Quote from: tggzzz on May 29, 2017, 09:57:52 amAnd an even bigger shame when they can't see how finely tuned your code was to produce those exact screenshots.

author: tggzzz
author_rank: Super Contributor
timestamp: May 29, 2017, 10:42:46 am
content: Quote from: Fungus on May 29, 2017, 10:04:50 amAs has already been pointed out to you a pulse train with a low duty cycle scarcely constitutes "finely tuning", and is a common waveform in hard realtime systems. For example, on one of my other projects with this device the input period varies from 60ns to 6s.

author: Fungus
author_rank: Super Contributor
timestamp: May 29, 2017, 10:52:28 am
content: Quote from: tggzzz on May 29, 2017, 10:42:46 amGet back under your bridge.No "beginner" or non-troll would ever type this:Code:while (1) {outPort <: 1;outPort <: 1;outPort <: 1;outPort <: 1;outPort <: 0;...

author: MK14
author_rank: Super Contributor
timestamp: May 29, 2017, 11:19:22 am
content: I think both the OP's oscilloscopes, are beaten by this:It looks much cooler, can tell the time as well, and a situation can be carefully engineered, to make it look better than the original two scopes.

author: Gyro
author_rank: Super Contributor
timestamp: May 29, 2017, 11:27:09 am
content: That brings a whole new dimension to ground lifting!

author: David Hess
author_rank: Super Contributor
timestamp: May 29, 2017, 01:39:45 pm
content: Quote from: tggzzz on May 28, 2017, 11:32:02 pmThe DSO needs peak detection (1) to display this waveform correctly which the Rigol DS1000E series does not despite what its lying manual says. When I first evaluated Rigol's DSOs (before the DS1000Z series became available), I asked their customer service about it and just got more lies. "Of course they support peak detection, it is right there in the manual!" Having Rigol double down was very frustrating.My 27 year old 2232 DSO would have no trouble displaying this and it has done so. My slightly older 2230 might have problems because its peak detection only goes down to 100ns.I have no idea why the burst pulse is shown incorrectly on the DS1000E; that is just broken. The bandwidth is not high enough to reproduce the edges but the sample rate and bandwidth should be plenty for the peaks and where is that trailing edge trash coming from? That is not caused by low bandwidth or insufficient sample rate. I call shenanigans; that DSO is broken by design unless there is a problem with the probe.QuoteI have often made this measurement in real time systems. With a good oscilloscope you can measure the distribution of response time or latency and capture long latency glitches which completely destroy real time performance. If the distribution is gaussian, then you can even measure it quantitatively with a delta delayed sweep on an analog oscilloscope.Quote from: Fungus on May 29, 2017, 07:22:47 amThat is a good work around for an oscilloscope which has trouble making this measurement but instead of toggling, I set and reset so the pulse polarity is always consistent.QuoteMine does.Quote from: nctnico on May 29, 2017, 07:51:56 amThe Rigol DS1000E series does not support peak detection; it supports envelope detection over many acquisitions. Envelope detection should work for this and would even be preferable in some cases. From the user manual:Peak Detect Acquisition: Peak Detect mode captures the maximum and minimum values of a signal. Finds highest and lowest record pointsover many acquisitions.Quote from: nctnico on May 29, 2017, 08:46:16 amAnd then they may learn a more important lesson: Rigol's manuals lie!(1) Or a very long record length which will compromise performance. On the other hand, long record lengths are inexpensive and getting more so all the time.

author: 2N3055
author_rank: Super Contributor
timestamp: May 29, 2017, 02:40:03 pm
content: Quote from: David Hess on May 29, 2017, 01:39:45 pmDavid,I don't want you to think I defend Rigol. I don't.But.... Technically, you are wrong.. If THEIR User manual defines "Peak Detect mode" the way they do, they dont lie.They decided to define term "Peak Detect mode" differently than Tektronix or other US manufacturers.. It is sleazy (if deliberate), stupid, it is misleading at the first glance.. But not a lie.In documentation for the instrument they make it clear that they decided to call "Peak Detect mode" same thing that other manufacturers call "Envelope detection".And I agree with you, I hate when people don't stick with the standards, reinventing terminology, deliberately or not... They might decide to call Volt or Ohm something else too..Best regards,Sinisa

author: nctnico
author_rank: Super Contributor
timestamp: May 29, 2017, 02:49:17 pm
content: Peak-detect and envelope mode are not well defined so you have to read the manual to see what it actually does. Things get interesting when both peak detect and envelope mode are supported.

author: David Hess
author_rank: Super Contributor
timestamp: May 29, 2017, 03:11:27 pm
content: Quote from: 2N3055 on May 29, 2017, 02:40:03 pmI might forgive them for that if it was the only place Rigol did it but it was not. They systematically redefined several industry standard terms including peak detect, delay, delayed trigger (1) to make their product look good and then doubled down when I asked them about it insisting that their oscilloscopes supported functions which they do not.Further, they *changed* the definition when they released later oscilloscopes which do support peak detection. The Rigol DS1000E defines it one way and the DS1000Z another with the later being the industry standard for decades. So the old definition needed to be changed when they did not support it but once they supported it, the old definition was fine.Quote from: nctnico on May 29, 2017, 02:49:17 pmOffhand I do not know of any DSOs which support peak detection without also supporting envelope detection in one way or another but when tracking this down years ago, I ran across something funny.The documentation for the old Tektronix 2440 series calls it "glitch capture" but there is no such glitch capture or peak detect mode; there is only envelope mode. On these DSOs, peak detection in the traditional sense is always active when envelope mode is used and when you set the envelope mode to accumulate 1 acquisition, that is the same as peak detect mode on other DSOs and it does exactly the same thing. I just always found it odd that they did not include it as a separate mode or refer to it as peak detection.This threw me off when I was evaluating the DS1000E because I kept looking for a way to adjust the number of acquisitions in the displayed envelope to set it to 1 but there is no such adjustment and the hardware cannot support peak detection during decimation.(1) And I would add record length to that list as well. If measurements are made on the display record, then what is the actual record length?

author: 2N3055
author_rank: Super Contributor
timestamp: May 29, 2017, 03:29:34 pm
content: David,Thanks for explanation... Yeah, that's sleazy... I agree..I hate marketing tricks...Regards,Sinisa

author: tggzzz
author_rank: Super Contributor
timestamp: May 29, 2017, 04:07:11 pm
content: Quote from: David Hess on May 29, 2017, 01:39:45 pmI'm not overly interested in Rigol bashing per se; my points are more general and related to low-end digitising scopes in general.In this case I'll settle for envelope detection as being sufficient. That's also sufficient for measurement of the period (albeit with unnecessarily limited resolution on this particular scope).QuoteYes, and I don't fully understand that display either.It may be there is something I have missed deep in a menu; but since I'm scarcely a beginner if that's the case then it illustrates the problems that beginners can and do have.QuoteYes indeed.QuoteJust so.QuoteSo does mine, but I didn't want to further distract Fungus down unimportant alleys.

author: rstofer
author_rank: Super Contributor
timestamp: May 29, 2017, 04:37:13 pm
content: Quote from: Fungus on May 29, 2017, 08:43:38 amOr the lack of a screwdriver...

author: Paul Moir
author_rank: Frequent Contributor
timestamp: May 29, 2017, 05:01:26 pm
content: Quote from: tggzzz on May 29, 2017, 06:41:33 amSorry, I had it cranked way down to I think 50kHz but not for photographic purposes. I only had one 10x probe with me so the data channel is being served by one of those Ponoma minigrabber to BNC lead sets.EDIT: This was done on a Tek 465, a single beam scope. On data high rates I guess you couldn't view this. Chop won't work with fast signals and ALT will capture (likely) the next data packet rather than the one associated with the displayed SCLK signal. So DSOs are better after all!

author: David Hess
author_rank: Super Contributor
timestamp: May 29, 2017, 05:39:47 pm
content: Quote from: tggzzz on May 29, 2017, 04:07:11 pmI would not mind having a DSO or universal counter which can provide a histogram of the pulse timing but this is a high end feature and measurement cursors work well enough.

author: tggzzz
author_rank: Super Contributor
timestamp: May 29, 2017, 05:55:33 pm
content: Quote from: David Hess on May 29, 2017, 05:39:47 pmCuriously I'm using the XMOS and DevKit processor to count edges in two independent 16ns period bit streams (call them Fin and Fref, both 1Hz-15MHz), do some arithmetic to create two reciprocal frequency counters, and report the Fin/Fref results up a USB link to a host PC - all in software with no added hardware other than input buffers and protection diodes.When the "work of art" is "completed", I may move onto a statistical frequency counter. Your histogram doesn't seem so far removed from that

author: nctnico
author_rank: Super Contributor
timestamp: May 29, 2017, 06:22:02 pm
content: Quote from: David Hess on May 29, 2017, 05:39:47 pmMy GW Instek has some statistical functions which can analyse recorded segments and show a histogram using results from an automatic measurement.

author: Mechatrommer
author_rank: Super Contributor
timestamp: May 29, 2017, 07:25:00 pm
content: corporate specification: 200Mbps digital (square) signal, that is somewhere 2GHz BW or above...the corporate wise decision was... use 1GSps 50MHz BW obsolete model DSO...talking about choosing the right tool for the right job?ok ok the point was. higher BW analog can be had at cheap...ok point taken but... too many other points hidden...a very well known strategy try to take over the leader... distraction...show my 1 strong point, hide my other 100 weak points...ee is just not about seeing led blinking at 200Mbps...conclusion: never send a programmer to do engineers job...

author: tggzzz
author_rank: Super Contributor
timestamp: May 29, 2017, 09:03:43 pm
content: Quote from: Mechatrommer on May 29, 2017, 07:25:00 pmI'm not entirely sure what point you are making, but I refer you to paragraphs 2 and 6 in the first post ("The standard statement..." and "Before replying...").

author: Mechatrommer
author_rank: Super Contributor
timestamp: May 29, 2017, 09:29:46 pm
content: Quote from: tggzzz on May 28, 2017, 11:23:08 pm1) you are not using the right tool for the job...2) as a way of saying. hammer is bad than a screwdriver because hammer cant turn a screw.. all too often people saying hammer is better than screwdriver... whats missing isat putting nails into the wood3) hence yeah... (refer the colored statements)... the OP is full of contradictions and missing parts... this thread is a troll... someone should lock this down..

author: tggzzz
author_rank: Super Contributor
timestamp: May 29, 2017, 09:33:19 pm
content: Quote from: Mechatrommer on May 29, 2017, 09:29:46 pmSigh; there's definitely a lost-in-translation issue here, somewhere.

author: 691175002
author_rank: Regular Contributor
timestamp: May 29, 2017, 10:10:41 pm
content: For what its worth, when I was looking to buy an entry level scope analog just wasn't an option.For a complete beginner buying used equipment of unknown condition is a massive risk. Not only are you incapable of repairing problems (even simple ones) with the scope, but you don't even feel qualified to judge whether the scope is working properly in the first place.Used scopes can become pretty pricy outside of the USA, and spending that kind of money just doesn't seem smart when the 1054z exists.Now when you start looking to buy asecondscope many of the used analogs start to become very interesting.

author: tggzzz
author_rank: Super Contributor
timestamp: May 29, 2017, 10:20:25 pm
content: Quote from: joeqsmith on May 28, 2017, 11:41:09 pmI hadn't spotted that you had changed the contents of your posting, adding significant content.Bear in mind that my whole posting isnotrelated to expensive professional scopes, but is related to the class of cheap scopes frequently and forcefully recommended in this forum - and to what extent they are suitable for bit-bashed digital signals.What's the 7200's basic spec, particularly the front-end analogue bandwidth? Given that LeCroy is a long-standing decent professional brand, I would hope and expect that it would perform "without surprises". I don't see any surprises in the second screenshot.I don't understand what the Arb Generator screenshot is showing, and can't see the waveform it is generating. Certainly 400kHz is much slower than the waveform I generated (bit period 4ns). The voltage levels ought to be irrelevant.I don't understand what the last screenshot is showing, nor how it relates to the issue I've mentioned.If you are interested in hard realtime multicore parallel systems, the XMOS processors and xC are definitely worth understanding. Their pedigree (people, theoretical basis, practical experience) dates back to the 70s in the form of CSP, Occam, Links/Channels and the Transputer. Some of the concepts have found a place in very different systems, e.g. some TI DSPs.

author: tggzzz
author_rank: Super Contributor
timestamp: May 29, 2017, 10:36:44 pm
content: Quote from: 691175002 on May 29, 2017, 10:10:41 pmWe pretty much agree.A beginner should only have a working scope, of whatever type. Taking on a "restoration project" is only for those that enjoy doing that and are prepared to take some risks!If money is a serious consideration, which is likely on this forum, then it may be worth considering a very cheap very basic analogue scope. I don't know where you are based, but in the UK if you are patient you can find working examples at about £1/MHz, and frequently they are simply given away. (My local hackspace will shortly be throwing half a dozen out, unless members want them!)£20 for a 20MHz scope is a viable way to learn about scopes in general, and to find out what you really do and don't need, and why. Think of it as a cheap and valuable "learning experience" before you spend significantly more money.And I agree, while there's little point in having two very similar scopes (or tools), it can be worth having significantly different scopes (or tools) - so that you can use the unique advantages of each as appropriate. That's why I also have a new 10MHz (not 100MHz) digitising storage scope.

author: Specmaster
author_rank: Super Contributor
timestamp: May 29, 2017, 10:44:24 pm
content: I have been reading the arguments and counter arguments with much interest and I have to be completely honest and say that much of it is way above my level of understanding but speaking purely as a person who is effectively getting into electronics again after about a 40 year break and also maybe from a different perspective to some of the members contributing to this thread. My interest lays in the ability to do relatively simple things like fault find on broken items of consumer electronics such as radios etc then it becomes a simple choice, spend a little (especially when your like me, retired on a fixed income) or if you can afford it go for something with all the bells and whistles on it such as a DSO. A cheap analogue scope is just as capable of telling you if the item under test be it a transistor, valve or an IC etc is A/ receiving an input and B/ giving an output and that I would suggest is basically what an awful lot of people really require. Anything else is in some cases is just guilding the lily, i.e. nice features to have but how often will the extra functionality be used or indeed actually required.The scope needs to be matched to likely and expected work it is going to be used on and I can't help but think that sometimes features on scopes etc are for a lot of people, like features on cars, bragging points that can used in a game of top trumps. My car has a TV built in and surround sound cinema system, great for bragging rights but how often have I used it, about once in 4 years of owning the car.

author: tggzzz
author_rank: Super Contributor
timestamp: May 29, 2017, 11:08:05 pm
content: Quote from: Specmaster on May 29, 2017, 10:44:24 pmThat is an absolutely key point that many people on this forum repeatedly mention - and many people dogmatically don't mention. The aphorism in my .sig has direct analogies with electronics, as your posting indicates you already knowApart from that, "welcome back". It is off-topic, but you'll find many things have changed depressing little; the fundamentals are still more or less the same. The major differences are a smaller, much cheaper, and significantly faster. Embedded computers haven't changed: still mostly C on 8/16/32 bit single-core machines. The major technology revolutions are in the speed/resolution of affordable ADCs and DACs, and nano-power technology.

author: joeqsmith
author_rank: Super Contributor
timestamp: May 29, 2017, 11:36:15 pm
content: Quote from: tggzzz on May 29, 2017, 10:20:25 pmRight, I read what you wrote and understood. Just thought I would inject something in my holding place.The Arb screenshot is some crappy app I put together to drive my old Sony. The waveform is shown in the bottom of the screen.Now we come to the fundamental problem. I had assumed you knew how to read a scope. You are at 20ns/div. I also show 20ns/div. Count the number of cycles per division on my screen shot and what do you see? Maybe that I am actually running a little faster than you, not slower.In your original post you stateQuoteThe last screen shot shows a rise and fall time (10/90) of 1.3ns. Those digital readouts must have thrown you off.Anyway, I wanted you to see that it was in the ballpark (slightly faster edge) than what you show.The 7200 is a modular scope. The 7242B w/50 ohm coupling has an analog BW of 500 MHz. Looking at the edge rates, I was using the 7262 which has a 4GHz bandwidth, 10 bits vertical and 100GS/s (RIS).As I mentioned, I gave away my one Lecroy that was much nicer than this one. There is no color LCD screen so not much value to the beginner. I bought the Hitachi brand new and rarely ever used it after I bought this old LeCroy. The only advantage the Hitachi had was weight and size.**** Small update ****Just in case there was some question about how the old relic would handle the 10ns pulses at 10KHz in single shot. I figure 12ns ish was close enough for you.In case you missed it, I also attached a screen capture of what I did to simulate your pattern test.

author: David Hess
author_rank: Super Contributor
timestamp: May 30, 2017, 12:00:34 am
content: Quote from: tggzzz on May 29, 2017, 10:36:44 pmThis is the big problem. There are lots of good used and inexpensive analog oscilloscopes out there but the people who could make the best use of them do not have the experience to recognize or maintain them.For this reason, I usually end up recommending the Rigol DS1000Z or similar despite my misgivings unless they have someone who can help them find a less expensive alternative.QuoteDespite being a big believer in this, I still have duplicate oscilloscopes but only because I end up fixing every one of them.

author: snoopy
author_rank: Frequent Contributor
timestamp: May 30, 2017, 12:23:13 am
content: Quote from: tggzzz on May 29, 2017, 06:31:45 amThe bandwidth of this Rigol scope is only 50 MHz and your analog scope is 350-400MHz ? That in itself a huge discrepancy !!Good luck to you if you find your analog scope more useful for measuring protocols and counting bits. You'd be the exception to the rule.

author: lem_ix
author_rank: Regular Contributor
timestamp: May 30, 2017, 12:43:13 am
content: Your definition of beginner seems a bit different to what we usually experience on the forum imo.This hypothetical beginner has grown past the arduino/raspi. Doesn't use a breadboard. Understands that using a probe aligator clip doesn't give sensible measurements in many cases. Knows about probe impedance, lo-z probes and can make them or has them available. But is somehow confused about rise time and signal bandwidth and thinks those Mhz numbers printed on the scope are just a doodle. Somewhat unrealistic if you ask me and doubtful if such a measurement actually matters much for a beginner. Members that actually show some knowledge get recommendations more tailored to their needs. Also if someone is choosing between analog and digital, is it worth dropping all the benefits of a digital scope for this one case where the analog one is better?(not saying you shouldn't get both if you need bw cheaply)Digital scopes are the norm today, the only reason I would ever recommend an analog one is if someone needed cheap bandwidth for analog like work(Repetitive) and has the skills to repair one.Also analog scopes are not necessarily cheaper....Prices today from the local "Ebay" clone :Tektronix 466 - 323 EuroTektronix 5113 - 370 EuroHameg HM-203-6 - 290 EuroGoldstar OS-9020A - 320 EuroNeed I say more? Didn't know analog scopes were made out of gold. Sure this is not the case everywhere but do take that into consideration.Point being, while I sorta understand where you're going with this I find it terribly far fetched.

author: tautech
author_rank: Super Contributor
timestamp: May 30, 2017, 01:48:09 am
content: Quote from: David Hess on May 30, 2017, 12:00:34 amBingo.Quote from: lem_ix on May 30, 2017, 12:43:13 amBingo +2This is an art, deducing the experience of those seeking help and offering the right advice/solution.NO one solution fits all and while the many greybeards here would happily grab a CRO, for novices with little electronic and especially HV experience to advise them to spend money on a CRO is irresponsible.

author: tggzzz
author_rank: Super Contributor
timestamp: May 30, 2017, 08:17:37 am
content: Quote from: joeqsmith on May 29, 2017, 11:36:15 pmNo wonder it didn't mean anything to me, nor probably to other people.QuoteOh, I can. Notice that I didn't question the middle trace, since it that was obvious.The bottom trace looks like a sine wave without any clear indication of what's on each axis. I did not see why you were showing that.A terse explanation of why you are showing a picture (e.g. a title) is very helpful for your audience.QuoteThank you for the essential information allowing us to interpret what you are showing.This thread is about the standard advice given to beginners on this forum, to wit that a new low-end 50/100MHz digitising scope is all you need for bit-bashed digital signal, and that cheaper older analogue scopes are useless.You show a high-end professional 500MHz scope, so while all your statements are correct, they are not comparable.OTOH I would certainly agree that your LeCroy is more than adequate for that job, and, like you, I would advise a beginner to ignore the lack of a colour LCD display!

author: tggzzz
author_rank: Super Contributor
timestamp: May 30, 2017, 08:31:57 am
content: Quote from: snoopy on May 30, 2017, 12:23:13 amOf course it is! The point is that a £85 old scope has a much more faithful measurement (in significant respects) than a new £275 scope. While that's never the only consideration, it is significant.QuoteI don't know what you mean by "measuring protocols and counting bits". That scope (and many others like the Tek 2xxx ranges) measures time/frequency/voltage.When I want to interpret the analogue voltages as a character or number, no, I certainly don't use a scope for anything more than a trivial quick look. If I want to look at digital information then I use digital domain tools: logic analyser or printf statements.In this case I would beverysurprised if a protocol decode correctly interpreted the signal in the second post. And, quite frankly, itshouldn'tbe able to interpret it correctly since it appears to be an invalid digital signal.

author: tggzzz
author_rank: Super Contributor
timestamp: May 30, 2017, 08:39:04 am
content: Quote from: David Hess on May 30, 2017, 12:00:34 amAll true.The Rigols are good value for money, and sufficient for many purposes. But they are not as good as some people claim for some relevant use cases (bit-bashed signals).QuoteI'm trying to break that habit; it is difficult

author: nctnico
author_rank: Super Contributor
timestamp: May 30, 2017, 08:50:14 am
content: Quote from: tggzzz on May 29, 2017, 11:08:05 pmI start to see parallels with you repeating your objections against C++. The whole world seems to think differently.

author: tggzzz
author_rank: Super Contributor
timestamp: May 30, 2017, 09:03:35 am
content: Quote from: lem_ix on May 30, 2017, 12:43:13 amThere is, of course, a continuum and many people here are extremely knowledgeable. Anyone that knows the beneficial characteristics of loZ probes isn't a beginner! Apart from that, I believe I covered (and agreed with) your last point in paragraph 6 of my first post ("Before replying...").QuoteI don't disagree. Single shot is the killer advantage of digitising scopes. Analogue storage scopes always were a pain in the backside, and only used because there was no alternative!My posting indicates that low-end digitising scopes are misleading when looking at the outputs from low-end DevKits in simple use cases.QuoteOh, I can find much higher asking prices on fleabay! I've no idea why anyone would think of paying £650 for a 2465! If that was a realistic price I'd sell my 2465 like a shot!QuoteAs I indicated in the initial post, I deliberately "over egged" the position to make the point, and chose extreme - but realistic - examples. To that extent it isn't "terribly far-fetched", although it certainly is on the boundary.

author: nctnico
author_rank: Super Contributor
timestamp: May 30, 2017, 09:07:35 am
content: Quote from: tggzzz on May 30, 2017, 09:03:35 amAnd that is based on just one sample using an old DSO which has been deliberatly setup wrong too! Your posting would have been much more informative to beginners when it showed how to do the same measurement.

author: tggzzz
author_rank: Super Contributor
timestamp: May 30, 2017, 09:08:22 am
content: Quote from: nctnico on May 30, 2017, 08:50:14 amThat's an entirely different topic. If you believe the "whole world seems to think differently", then you have a blinkered weltanschauung. (30 years ago someone made similar statements to me about COBOL!)

author: tggzzz
author_rank: Super Contributor
timestamp: May 30, 2017, 09:19:49 am
content: Quote from: nctnico on May 30, 2017, 09:07:35 amThe 10kHz waveform deliberately used the "normal" acquisition setting. Iexplicitlydrew attention to the fact there are more appropriate settings. Personally I think that beginners would be helped if the "peak detect" (which isn't actually a peak detect, but that's a different point) was the first and normal setting.If there is a way the 0x005555ff waveform could be improved, let me know. If there is a significant improvement, I will show it.

author: joeqsmith
author_rank: Super Contributor
timestamp: May 30, 2017, 12:32:11 pm
content: Quote from: tggzzz on May 30, 2017, 08:17:37 am

author: tggzzz
author_rank: Super Contributor
timestamp: May 30, 2017, 12:56:28 pm
content: Your quoting seems a little cocked up; I believe I've corrected it. Never ever made that mistake, oh noQuote from: joeqsmith on May 30, 2017, 12:32:11 pmIt is easy to overestimate your audience!QuoteI deliberately omitted mentioning a specific scope since I wanted people to concentrate on the generic waveforms and performance, not on one specific scope.As you say, tech progresses - but in both instrument and circuit speeds.in yesteryears, bog-standard scopes (10MHz) weren't good enough for looking at bog-standard logic (74/74LS/etc) and embedded processor (8080/Z80/6809) outputs; a 465 class machine was necessarysimilarly, now a bog-standard (50/100MHz) digitising scope isn't good enough for looking at bog-standard logic (74LVC/etc) and embedded processor (e.g XMOS xCORE) outputs; a 350MHz(ish) machine is necessaryBut, at the moment, there is an overlap where reasonably priced analogue scopes offer a significant advantage in the important use-case of bit-bashed processor outputs.My objection is to people that refuse to acknowledge that, often wrapped up in a newer-is-always-better mentality.

author: Fungus
author_rank: Super Contributor
timestamp: May 30, 2017, 01:35:47 pm
content: Quote from: tggzzz on May 30, 2017, 12:56:28 pmYep. Everybody should be buying old analog 'scopes based on a single pathological case that's easy to avoid.(not that a newbie would ever type that trollcode anyway)

author: tggzzz
author_rank: Super Contributor
timestamp: May 30, 2017, 01:49:20 pm
content: Quote from: Fungus on May 30, 2017, 01:35:47 pmExcellent - please enlighten us as to how you think the 0x005555ff example can be avoided. I'll try it and if there is a significant improvement, I'll show it.QuoteYou've already implicitly acknowledged that is an irrelevant detail; repeating the statement doesn't show you in a good light.https://www.eevblog.com/forum/testgear/old-analogue-scopes-beat-new-digital-scopes-for-bit-bashed-digital-outputs/msg1220024/#msg1220024

author: David Hess
author_rank: Super Contributor
timestamp: May 30, 2017, 02:50:34 pm
content: Quote from: snoopy on May 30, 2017, 12:23:13 amBut that 50 MHz DSO should still be faithfully reproducing the signal within the constraints of its 50 MHz bandwidth and it is not doing that; there are signal artifacts, especially on the trailing edge but also at the beginning of the pulse train, which simply do not exist. The 350 MHz oscilloscope result simply shows what should not be there; the DS1052E is displaying something which does not exist.I actually find it difficult to believe that the 50 MHz DS1052E (or any oscilloscope) produced that result unless it was broken; to me it looks more like a probe problem. tggzzz, your original post says that you used a 1.5GHz Z0 (low-z?) probe but could you describe the probe in more detail? How was it connected to the DS1052E? Was it through the needed feedthrough termination? It should not matter but was the same feedthrough termination used on the 2465 or was its internal termination used? Could the DS1052E have been damaged before the test?

author: Fungus
author_rank: Super Contributor
timestamp: May 30, 2017, 03:41:56 pm
content: Quote from: tggzzz on May 30, 2017, 01:49:20 pmNope.Setting the clock to 250MHz and outputting one '1'obviouslythe same as setting it to 1000MHz and outputting four '1's.If you were interested in anything other than trolling you'd have said something like "I had to output X 1's to get it the pulse to show on the 50MHz DSO when 4 was enough on the analog scope with six times the bandwidth".I suspect X might be 5, because 4 isalmostshowing on the DSO. Why don't you change the code to output five 1's for us...?

author: joeqsmith
author_rank: Super Contributor
timestamp: May 30, 2017, 05:19:43 pm
content: Quote from: tggzzz on May 30, 2017, 12:56:28 pmSeldom review what I post. It would take me too long to correct all my mistakes.Quote from: tggzzz on May 30, 2017, 08:17:37 amRight, I can understand your point. The only thing I am suggesting is that there may be reasonably priced vintage DSOs that would also offer some pretty big advantages over an analog or low end DSO.

author: tggzzz
author_rank: Super Contributor
timestamp: May 30, 2017, 05:38:03 pm
content: Quote from: joeqsmith on May 30, 2017, 05:19:43 pmWe are in violent agreementMy only caveat would be that recent DSOs are usefully more mature and usable than some of the earlier DSOs. Examples would include 1GHz 25MS/s scopes (top of HP's range at the time!), and (less seriously) scopes where vertical sensitivity changes are via the "calibrate" softkey. That doesn't invalidate your point, it merely alerts people that more care is taken in selecting such a scope.

author: free_electron
author_rank: Super Contributor
timestamp: May 30, 2017, 06:44:04 pm
content: why are we using an oscilloscope to check timing of digital systems in the first place ? that's what logic analyzers with state/timing analysis were designed for...

author: tggzzz
author_rank: Super Contributor
timestamp: May 30, 2017, 06:57:19 pm
content: Quote from: free_electron on May 30, 2017, 06:44:04 pmI wish more people thought like that! Scopesshouldbe used to ensure signal integrity, and thereafter debugging should flip to the digital domain.In this case the reason is twofold: the traditional statements on this forum w.r.t. analogue vs digitising scopes and their uses, plus the 250Mb/s 4ns serial bit rates bashed out of the processor.

author: Fungus
author_rank: Super Contributor
timestamp: May 30, 2017, 07:02:55 pm
content: Quote from: tggzzz on May 30, 2017, 06:57:19 pm...which you tried to look at on an old 50MHz DSO before pronouncing your verdict.

author: tggzzz
author_rank: Super Contributor
timestamp: May 30, 2017, 07:18:03 pm
content: Quote from: Fungus on May 30, 2017, 07:02:55 pmRead what I wrote in the first post, concentrating on the second paragraph "The standard statement...". Other people seem to be able to understand that, and to be able to concentrate on the essential points.

author: Fungus
author_rank: Super Contributor
timestamp: May 30, 2017, 07:45:52 pm
content: Quote from: tggzzz on May 30, 2017, 07:18:03 pmWell:a) It's usually applied to the 100MHz DS1054Z, not an old clunker of a "Rigol"andb) You still haven't posted a screenshot of what happens if you output more than four 1's in your program.

author: kcbrown
author_rank: Frequent Contributor
timestamp: May 30, 2017, 07:52:39 pm
content: Quote from: tggzzz on May 30, 2017, 08:39:04 amWellof coursethey're not as good for bit-banged signals if the analog characteristics of the signal fall outside the analog capabilities of the scope! That doesn't make the analog scope the proper tool for the job, however, especially since the analog scope doesn't have single-shot capture capability, much less protocol decode capability (we're talking about beginners here -- how many of them are going to be interested in manually decoding the signal they see on the screen when they don't have to?). And yes, a logic analyzer is a better tool for doing protocol decode, but if you're trying to track down an analog domain glitch in your digital signal, having the decoded data for context at the same time you see the glitch on the screen may prove invaluable, no?The Achilles heel of the analog scope is the lack of single-shot capture -- now you're dependent upon a quickly (in human terms, at least) repeating pattern, which may or may not be reasonably possible to generate, to make it possible to see anything at all.As you noted in your original message, the proper tool depends on the context. Context matters,a lot, and that is just as true of the advice generally given to beginners as anything else.I expect that the advice given to most beginners is based on the presumption that they'll be using lower speed microcontrollers (Arduino and the like). The microcontroller you're using is amongst the faster ones, with (if I'm not mistaken) an internal clock of 60MHz (I wasn't able to find a datasheet on the processor your development board uses, and had to guess on the basis of the number of cores and the total MIPS, as described in the hardware manual for your board:https://www.xmos.com/download/private/startKIT-Hardware-Manual%281.3%29.pdf.And that presumes one instruction per clock per core).Also, the scope that is usually recommended today (the Rigol DS1054Z) might or might not show some of the erroneous artifacts that your digital scope is showing, particularly since it claims to have real peak detect.And finally, the digital scopes that are available to beginners and that are within their usual budget are getting faster. See, e.g., the Siglent SDS1202X-E (which has 200MHz bandwidth).Now, I've definitely noticed the trend towards faster microcontrollers, but even so, we're talking aboutbeginnershere. They'll tend to be using whichever platform has the best community support precisely because they're beginners and will benefit more from that support than they would from using a faster, but more esoteric, microcontroller solution. That platform is currently the Arduino. There are some, e.g. the STM32, which are getting better, but the Arduino is the mainstay for now.If a beginner is doing bit banging at a rate that exceeds the capability of the Rigol DS1054Z (at least in hacked form), then he's either unusual or he's notreallya beginner, at least in the sense I'm thinking of.

author: tggzzz
author_rank: Super Contributor
timestamp: May 30, 2017, 07:55:49 pm
content: Quote from: Fungus on May 30, 2017, 07:45:52 pmSigh. According to the Rigol website, the ds1054z is 50MHzhttps://www.rigol-uk.co.uk/Rigol-DS1054Z-Digital-Oscilloscope-p/ds1054z.htmDo you have anything helpful to contribute this conversation? Since other people manage to achieve that, I'm left wondering what your motivation is.Anyway, I'll respond to anyhelpfulcomments you might make in future.

author: Mechatrommer
author_rank: Super Contributor
timestamp: May 30, 2017, 07:58:23 pm
content: Quote from: tggzzz on May 30, 2017, 06:57:19 pmsuggesting a 350MHz CRO to beginner to ensure signal integrity of a sub ns risetime signal is ridiculous..

author: ebastler
author_rank: Super Contributor
timestamp: May 30, 2017, 07:59:41 pm
content: Quote from: kcbrown on May 30, 2017, 07:52:39 pmI'm pretty confident that any beginner has long since stopped reading this rather childish exchange.(Not talking about you, kcbrown, but the two grumpy old men carrying on this sorry thread...)Jeez, this started as a way to get tggzzz over a boring Sunday afternoon, but it's Tuesday now!

author: 2N3055
author_rank: Super Contributor
timestamp: May 30, 2017, 08:03:24 pm
content: I apologize for being daft, but would you please explain what do you want to prove here..I read first post several times (my english is not very good) and I think that you wanted to prove following statement:"I think it is wrong to give too generalized advice to beginners what first scope to buy.Everybody seem to say that very low end digital scopes are always better than good used high end analog scopes.That is not true.Digital scopes do have many good functions that analog scopes don't have, but these days some of the small CPU development boards work at such frequenciesthat these toy 50MHz scopes won't work. Old analog scope that is not best tool for digital work, but if it has enough bandwidth you will be at least able to see something undistorted.And by clever technique, you might even be able to do the work, as opposed the toy scope that will not be useful at all at those frequencies and signals. "Is that it?Because if that is what you think I agree 100%.But you yourself used wrong GENERALIZATIONS to prove it...1. Average low end dev kit is Arduino or something like that. Definitely not something that has high speed SERDES interface on it..2. NOBODY recommends DS1052E to anybody, since like 3-4 years ago.. Recommendations for entry level are DS1054Z, or Siglent SDS1202X-E, orolder good analog scopes if you can get good one for cheap.You cannot make DS1054Z make that waveform that you show, even the 50MHz version one... Siglent SDS1202X-E is 200MHz, definitely would work for this just fine.3. Where I live you cannot get good old high end analog scope for the money you are saying. There aren't any, and importing, shipping and handling and crap like that it gets to 800-1000€ easy..NO, we are not retarded, we just live in places where there isn't a good second hand market for T&M equipment...So I'm really confused.. You tried to relay a good point that I agree with 100%, by choosing methodology that is wrong.For this particular case I would recommend a Siglent SDS1202X-E because it is 200MHz. Although, I think DS1054Z would show usable info too...Best regards,Sinisa

author: kcbrown
author_rank: Frequent Contributor
timestamp: May 30, 2017, 08:04:43 pm
content: Quote from: ebastler on May 30, 2017, 07:59:41 pmWell, seeing how the original message was about advice given to beginners, I think the real target audience is those who are giving advice, not the beginners themselves. Can't say whether advice-givers are still reading the thread.

author: Fungus
author_rank: Super Contributor
timestamp: May 30, 2017, 08:06:05 pm
content: Quote from: 2N3055 on May 30, 2017, 08:03:24 pm

author: tggzzz
author_rank: Super Contributor
timestamp: May 30, 2017, 08:13:56 pm
content: Quote from: kcbrown on May 30, 2017, 07:52:39 pmThose are fair points, and I have no strong arguments with them.The scope I'm using does have "peak detect" (ahem), and as I indicated, it does indeed give the stable result you would expect - unlike the "normal" setting. IMNSHO, envelope detect ought to be the normal mode.Your point about the Arduino ecosystem's attraction for beginners is correct and important. Personally I find the StartKit easier to program than the Arduino, but that isverysubjective and dependent on the problem at hand.The XMOS processor in the StarKit is one of their low-end ones; according to DigiKey they go up to 32 cores and 4000MIPS. The StartKit is about half the price of a bog-standard Arduino (~£26/£12). Hence I feel justified in regarding the StartKit as "beginner level".

author: tggzzz
author_rank: Super Contributor
timestamp: May 30, 2017, 08:26:27 pm
content: Quote from: 2N3055 on May 30, 2017, 08:03:24 pmYes, to a good approximation.QuoteI made somespecificpoints,with caveats, and used them as an examples of more general issues.QuoteSee my previous response (written after you posted this) as to why I think it can be justified.QuoteToo many of the comments on this forum completely dismiss working old analogue scopes; that's wrong. I'm not aware of specific differences between the 1052 and 1054, but the Rigol website says they are both 50MHz.QuoteI don't see why you wouldn't see the same thing with a 1054. I have no comment about the 1202; clearly 200MHz ought to help.As for price in your location, clearly that is a very important factor - and I would almost certainly come to the same conclusion.QuoteThank you for some thoughtful points.

author: kcbrown
author_rank: Frequent Contributor
timestamp: May 30, 2017, 08:30:14 pm
content: Quote from: tggzzz on May 30, 2017, 08:13:56 pmBut it apparently doesn't function the way one would normally expect it to, whilst the DS1054Z's apparently does (assuming, of course, that the feature actually behaves the way the manual describes. I expect we would have heard complaints about itlongbefore now if it didn't).Quote"Beginner level" for a piece of hardware isn't measured by hardware capability within its family line, it's measured by the ease with which someone who doesn't know the first thing about these things can jump in and learn how to make it do his bidding. That's determined by a number of things, such as the amount of support in the community there is for it, the availability of hardware and software for it, the availability of example code, etc.If the XMOS StartKit were the most popular and well-supported microcontroller development platform out there (i.e., if it occupied the place the Arduino currently occupies) then your objection to the standard advice given to beginners would be a lot more valid. But then, if that were the situation,the advice given to beginners would be much different from what it currently is. Context matters.Interestingly, though, if that were the actual situation, then I suspect higher-bandwidth entry-level scopes would have come onto the scene earlier simply due to the demand. I suspect that, as microcontrollers get faster, the entry level T&M hardware will get faster to match. We're already seeing some of that right now.

author: tggzzz
author_rank: Super Contributor
timestamp: May 30, 2017, 08:40:36 pm
content: Quote from: David Hess on May 30, 2017, 02:50:34 pmA sensible doubt, sensible observations, and sensible questions.Probe: HP10020A.50ohm termination: Greenpar BNC inline/feedthrough which ought to be good to at least a GHz. I haven't seen such effects when I've used them in the past, but that is a weak statement.Rigol damage: I've borrowed the Rigol, but I believe it hasn't been used much. I've no reason to believe damage, and both channels are the same.2465: internal termination.Like you I think feedthrough-vs-internal termination "should not matter", but that is undoubtedly an unnecessary extra variable. I'll check it at the earliest opportunity (not tonight).Unfortunately I haven't got any active probes to use as a comparison, and I certainly wouldn't trust my high impedance passive probes with a 1ns edge rate.

author: Mechatrommer
author_rank: Super Contributor
timestamp: May 30, 2017, 08:46:41 pm
content: Quote from: tggzzz on May 30, 2017, 08:26:27 pmthen you missed the long memory, 4 channels and level graded display. i hope the 1052 you are testing is the hacked unit to 100MHz, otherwise you just proved you ignorance. its ok you may carry on, your english is too good that nobody can understand, you may play with your bit-bashed signal integrity to the next weekend through your phosphor graded CRO.Quote from: kcbrown on May 30, 2017, 08:30:14 pmhow many beginner's level (cheap) I2C or SPI chips you see today that's necessitate 200Mbps rate? (or even close to it)

author: kcbrown
author_rank: Frequent Contributor
timestamp: May 30, 2017, 09:04:33 pm
content: Quote from: tggzzz on May 30, 2017, 08:26:27 pmThe DS1054Z is easily hackable to 100MHz. I believe the same is true of the DS1052E.The differences between the two are quite substantial. For instance, the DS1054Z is (with the right settings) capable of a waveform update rate in the 30,000 per second range.QuoteYou're making a lot of presumptions here. The sampling rate of the DS1054Z is 1GS/s. The frequency response of the DS1054Z doesn't just fall off a cliff after 50MHz. See this thread for more details:https://www.eevblog.com/forum/testgear/pulse-generator-rise-time-and-rigol-ds1054z-bandwidth/The frequency response of a typical DSO is not Gaussian:http://literature.cdn.keysight.com/litweb/pdf/5988-8008EN.pdf

author: 2N3055
author_rank: Super Contributor
timestamp: May 30, 2017, 09:08:59 pm
content: DS1000Z series has 24 times the memory depth than DS1000E series. It has much more advanced acquisition engine that has real "Peak detect" (single shot).Also most people "unlock it" to 100MHz version (it is sort of something Rigol seems to not mind for hobby use), in which case it has pretty much 120MHz+ -3dB bandwidth.So I think it would show your example reasonably enough, though edges would not be as clean...But I would like to point out, that most of beginners ( and professionals too, on simpler projects) are mostly monitoring communication from CPU to peripheral chips, using SPI, I2C, 1-Wire, RS232 and RS485 (async serial, at low speeds up to 115200 bps) and such.. No SERDES connected high speed A/D or D/A converter running 10s or 100s of MS/Sec.. That is an advanced project, with serious DSP code behind it and such...Regards,Sinisa

author: kcbrown
author_rank: Frequent Contributor
timestamp: May 30, 2017, 09:24:38 pm
content: Quote from: Mechatrommer on May 30, 2017, 08:46:41 pmYou don't,yet. But with a general-purpose DSO, that's not the only kind of thing you'd be interested in anyway. It's a general purpose tool, which means you'd be using it to see all sorts of things. The faster the microcontroller, the closer the spacing of digital signal events that you're likely to be interested in.Now, there's something that hasn't yet been mentioned but which is quite important. And that is that it's probably not an accident that entry level microcontrollers are relatively slow. The faster the microcontroller, the faster your T&M equipment has to be in order to really keep up. But perhaps more importantly, the faster the microcontroller and the signals it produces, the greater the importance of the analog transmission line characteristics of the links carrying those signals. Get fast enough and proper endpoint termination, as well as signal leakage, etc., becomes very important. And perhaps most important of all for a beginner,you can no longer use breadboards for prototyping if your signals are fast enough.Which is to say, ease of experimentation is also amonumentallyimportant consideration. Having to solder up a protoboard, and especially to do so while considering things like the crosstalk characteristics of parallel signal lines, is something that is well beyond any real beginner, and yet that's exactly what you have to deal with once your data rates get high enough (100MHz territory, from what I'm reading).For these reasons, I don't expect beginner territory to change all that radically even if microcontrollerscanbe faster.

author: Fungus
author_rank: Super Contributor
timestamp: May 30, 2017, 09:59:47 pm
content: Code:while (1) {outPort <: 1;outPort <: 1;outPort <: 1;outPort <: 1;outPort <: 0;..."First thou pullest the Holy Pin. Then thou must count to four. Four shall be the number of the counting and the number of the counting shall be four. Five shalt thou not count, neither shalt thou count three, excepting that thou then proceedeth to four. Six is right out. Once the number four, being the number of the counting, be reached, then lobbest thou the code in the direction of thine DSO, who, being naughty in my sight, shall snuff it."

author: xrunner
author_rank: Super Contributor
timestamp: May 30, 2017, 10:04:10 pm
content: Quote from: Fungus on May 30, 2017, 09:59:47 pm

author: rstofer
author_rank: Super Contributor
timestamp: May 30, 2017, 11:07:31 pm
content: Having come from a 10 MHz scope prior to my Tek 485, I had to come up with some tricks to figure out how to display things that were beyond the bandwidth.One approach that always works is to slow down the clock. Get the system to work and then see what happens when the clock is restored. Does it still work?Another approach is to code simple loops over the offending peripheral. Even with the 485, I can't see an SPI transaction that occurs once per second with a clock of 10 Mhz. It's done and gone before the trace is even visible. Loops help. So does a DSO with single shot mode.XMOS seems cool, I might find an application for it some day. It's a beginner level device in the same way an FPGA is a beginner level device. It depends on where you are beginning from. There are some folks who majored in hardware design in grad school...The OP has been around here a long time (over 5,000 posts) so it seems a little disingenuous to not know that the DS1054Z is easily, and properly, unlocked to 100 MHz. It's not a hack, it's not hardware changes, it is simply selecting a different analog filter that is known to exist. A feature designed into the hardware so the same device could be sold with two different bandwidths. He knows this but chooses to ignore it.It's tough to recommend a scope to a real beginner - one without an MS in hardware design, for example. Yes, an analog scope will work but... It will have no features in comparison to a DSO. It may, or may not, work and stay working. The buyer may, but probably won't, be able to fix it. Beginner, remember? And no warranty!Beginners can't even spell bandwidth much less understand the implications when thinking about square waves. Odd harmonics? What's that about? I need how many? Well, how many are there? Und so weiter.Then they show up with a minimal budget. A used analog scope is the only alternative. Now it's just a matter of making the least bad choice from what is available. And hoping... Hoping is good but not always helpful.And then there is the cost of shipping...I just don't have a recommendation for someone with a $100 budget. Once those school scopes are gone, there may not be any decent choices.I like the idea of the SDS1202X-E and I'm waiting for the first firmware upgrade. After several upgrades the DS1054Z is stable. There's still a spelling error but I'm falling into the 'inside joke' camp. Who cares?Unless the beginner has a specific need for a much higher bandwidth, I'm sticking with these. If they need bandwidth and they don't have money, I guess it's off the eBay and seeing how it all works out. The beginner can work for decades with microcontroller projects and not outrun the DS1054Z. Even FPGA projects seldom toggle pins beyond 50 MHz. Yes, the SDS1202X-E would be a better choice in this case.And, yes, I expect the Arduino to be the uC of choice for beginners for a very long time. There's a ton of projects on the Internet and a lot of support groups.

author: Mechatrommer
author_rank: Super Contributor
timestamp: May 30, 2017, 11:16:02 pm
content: Quote from: kcbrown on May 30, 2017, 09:24:38 pmyup except that when you expect a 50-100MHz 1GSps scope to show good fidelity on 1-2ns rise/fall time, then its just ridiculous. not to mention invalid setups to prove a point where in one measurement, ringing (on the falling edge) is much more prominent in the said DSO. here look again... with the right mind we should expect some illusive aliasing (wave superimpose) on the signal packet... signal dis-integrity due to questionable measurement setup.

author: tautech
author_rank: Super Contributor
timestamp: May 30, 2017, 11:26:36 pm
content: Quote from: rstofer on May 30, 2017, 11:07:31 pmThis.

author: MK14
author_rank: Super Contributor
timestamp: May 30, 2017, 11:39:43 pm
content: I DON'T agree that the analogue scope is so useful for signal integrity (as regards rare phenomenon). Because there can be occasional and super rare events such as glitches/transients/metastability etc which can flip bits (to incorrect states), when they occur. But may be very difficult to detect with analogue (non-storage tube and/or digital) oscilloscopes.With a digital scope (with sufficiently powerful enough capabilities), it can be triggered (one-shot), when the MCU (or FPGA or whatever), detects bit errors, bit collisions, etc.These may be extremely rare (e.g. metastability), and take many hours to occur (trigger).Nevertheless, these issues need to be sorted, in order for the hardware to work properly, in most cases.The top MCU (that the OP seems to be using), can go to a claimed 4000 MIP's. I don't know its clock frequency, but that COULD be 250 pico seconds (4 GHz). So I can imagine the OP, with a signal mostly at 0, but at 1 for just 250 pico seconds, with him trying to display it on a 50 MHz oscilloscope. Then creating another thread, complaining about why he can't see his 250 pico second signal, on his borrowed 50 MHz oscilloscope.tl;drThere are some very good reasons why, analogue oscilloscopes (brand new), have partly or fully disappeared from the market place.

author: tggzzz
author_rank: Super Contributor
timestamp: May 31, 2017, 12:14:11 am
content: Quote from: Mechatrommer on May 30, 2017, 11:16:02 pmIt would indeed be ridiculous.But for reasons best known to yourself, you have chosen to ignore paragraph 4 in the first post "The first point...". Hence your point is a strawman argument.QuoteThat's incoherent technobabble; clearly something has been lost in the translation.

author: rstofer
author_rank: Super Contributor
timestamp: May 31, 2017, 12:18:50 am
content: Quote from: kcbrown on May 30, 2017, 09:24:38 pmWe already have uCs that are very much faster than the Arduino. The Blackfin is about 600 MHz and it isn't even in the running for FAST. But you're right, they aren't for beginners. The learning curve is high and steep.What the Arduino has going for it (as the Basic Stamp had before the Arduino came along) is reasonable performance and a tremendous support group. Programming the device is made easy by the library code and there are thousands of example projects on the Internet (no, I didn't count them!). OTOH, the Parallax Basic Stamp is probably the best documented uC ever sold. Parallax has wonderful documentation.Experienced users kind of chuckle at Arduino users but that Arduino is a heck of a lot faster than the IBM 1130 I programmed back in '70. And it was state of the art for entry level minicomputers.Unless there is a major shift in thinking, I see the Arduino as the beginner's CPU of choice for a very long time.

author: tggzzz
author_rank: Super Contributor
timestamp: May 31, 2017, 12:24:51 am
content: Quote from: rstofer on May 30, 2017, 11:07:31 pmWhen peripherals and system operation allow it, and the source code is available allow, yes those are good standard techniques.QuoteYes indeed; the killer use-case for digitising scopes. Analogue storage scopes always were a pain in the rear endQuoteThe XMOS devices are muchmucheasier to "get into" than FPGAs. If you want to do two things at once in an MCU, then thr XMOS devices are also easier than learning an RTOS.QuoteI am aware of it, but it is non-standard and I don't have such a hacked scope. I cannot test it to see its effectiveness or otherwise.QuoteYes, the ecosystem is of critical importance - that's why the 80x86s are still dominant.

author: tggzzz
author_rank: Super Contributor
timestamp: May 31, 2017, 12:36:50 am
content: Quote from: rstofer on May 31, 2017, 12:18:50 amYes, and interesting.I wasverypleasantly surprised at how easy it is to create things in the XMOS world. That is partly because the theoretical concepts (CSP) are so simple and obvious - and usable in practice.From downloading the development environment to the first version of my software-only frequency counter (2*6MHz input frequencies) with the results being displayed on the host PC's screen was 1-2 days effort. I wouldn't have been able to do that any faster on the Arduino. Add another couple of days learning about the hardware and debugging mechanisms, experimenting and tweaking, and it is up to 2*15MHz.QuoteAgreed.When I returned to embedded programming via Arduinos, I was simultaneously satisfied and depressed at how little had changed in 20-30 years. The XMOS devices are definitely a change for the better, both hardware and software.

author: tggzzz
author_rank: Super Contributor
timestamp: May 31, 2017, 12:54:10 am
content: Quote from: MK14 on May 30, 2017, 11:39:43 pmYes, but digitising scopes don't make that any easier. The problem is finding a suitable trigger/detector, and then waiting!QuoteJust so.QuoteI don't know how the XMOS marketing department came up with the 4000MIPS! They've mentioned "dual issue", but I don't think the StartKit processor cores have that.However the XMOS devices can up to 32 cores each running at ~100MHz. Given that they have effectively embedded CSP in hardware (think of CSP as removing the need for an RTOS), all cores run independently and simultaneously except when they synchronise to exchange information over a "channel". The result is you can dedicate a separate core to controlling each peripheral; when there's nothing to do the core simply halts - and then restarts with latencies in the nanoseconds. FFI see XMOS literature.The I/O runs at up to 250Mb/s.QuoteYes indeed, but that doesn't mean that decent working analogue scopes should be ignored. There is a gap, constantly changing, where they are a very viable option.

author: kcbrown
author_rank: Frequent Contributor
timestamp: May 31, 2017, 01:14:21 am
content: Quote from: tggzzz on May 31, 2017, 12:14:11 amYes, but if you're talking about a modern microprocessor (hey, those were your words, not mine), then you're talking about a GHz-level device. Even your 350MHz analog scope isn't going to be capable of dealing with one of those.QuoteI think we're all in violent agreement on your main point: choose the right tool for the job.What we'renotin agreement about is whether or not your example shows that an analog scope with higher bandwidth is a better choice than a digital scope with lower bandwidth for abeginnerto use with digital signals. Yes, the analog scope cantheoreticallyshow the problems with the signal integrity of your example, butin practiceit will be difficult (verydifficult, I'd wager) for a beginner to use an analog scope for that purpose unless the glitch itself isveryrepeatable (i.e., shows itself many, many times per second). Put another way, for digital signals, the analog scope is probablynotthe right tool for that job, even if it might have enough bandwidth.Absent those very specific conditions that make the analog scope workable at all, the real takeaway here is that if you are working with signals where the pulse rate is in the tens of MHz (more precisely, where the bandwidth requirements of the signals are high enough that the bandwidth or sampling rate required to see glitches would exceed what the scope is reasonably capable of capturing), then you need a scope with greater bandwidth and sampling rate than the entry-level scopes that are typically recommended. And guess what? It also means that you have to start worrying about probing techniques and other things that most beginners haven't even considered.But if you're really working with such signals, chances are high you arenota beginner! Or, if you are, you're probably (way) over your head, because if your signals are that fast, you'll probably have to go to extra lengths to avoid signal integrity issues in the first place, lengths that you wouldn't even have to think about with hardware typically used by beginners, and you'll have to go to extra lengths to ensure that, firstly, your probing methods aren't introducing glitches into the signal and, secondly, that they are appropriate for the signals you're trying to evaluate.What this means, of course, is that one of the recommendations that must be given to beginners is that they work with relatively slow hardware, precisely because doing that would allow them to concentrate on things other than how to avoid the problems introduced by the transmission line characteristics of signal carriers -- and would allow them to use breadboards and other convenient prototyping mechanisms, to boot.

author: MK14
author_rank: Super Contributor
timestamp: May 31, 2017, 01:31:23 am
content: Quote from: tggzzz on May 31, 2017, 12:54:10 amThey make it easier, because they can capture a single (erroneous/suspicious) event. As long as you can set up a suitable trigger. E.g. Failed CRC32 comms error, sets a port pin, which is used to trigger the digital oscilloscope.Hence you can potentially see the glitch/transient/metastabilty etc, which caused the bit error(s) in the high speed communications stream.Although there did use to be analogue storage scopes, which could do a similar function. Assuming their limited write speed was acceptable and the resultant image fade, would last long enough (e.g. it would probably reduce in focus/intensity/readability, after about 10 minutes or so, maybe less, maybe longer, in my experience) to see the error.Quote from: tggzzz on May 31, 2017, 12:54:10 amThese XMOS devices, seem very interesting. Some of what you have described (e.g. accurately switching port pins, on a timed basis), can be done with modern timer hardware, on many MCU's. These timers have their limits (e.g. one or two transitions, then they need new values from the MCU), so being able to do it in real time, on a dedicated core (if you can affordably have 8/16 or 32 cores, hence some can be dedicated for the hardware I/O).Interrupts on conventional MCUs, take time. So the very high speed nature of these XMOS devices, potentially allows them to perform well, in some problem areas. E.g. very high performance PWM applications, with complicated capabilities.Quote from: tggzzz on May 31, 2017, 12:54:10 amA good point.Analogy:Linear bench power supplies (although still potentially available brand new), are being increasingly replaced by modern switched mode power supplies. So if you want a linear bench power supply (because of its potential for low noise/accurate outputs, simplistic/easier repairability and are use to them, from older, past experience). Your best bet, might be to buy a nice used one on ebay (or elsewhere).So I agree, a decent used analogue scope, is useful for some people.

author: snoopy
author_rank: Frequent Contributor
timestamp: May 31, 2017, 01:47:34 am
content: Quote from: tggzzz on May 30, 2017, 08:31:57 amMost beginners aren't going to be decoding serial or SPI buses running at 50MHz. Most of the time they will be running at 1MHz so even that old Rigol will be more than adequate for the job.Also whilst you might pickup up one of those old analog scopes cheap if it doesn't work it can be a nightmare to fix and a huge repair bill as the old custom chips are no longer available and have to be scrounged from other scopes. It's really false economy to say that an old analog scope is good value just because it is cheaper than a new one.

author: David Hess
author_rank: Super Contributor
timestamp: May 31, 2017, 01:59:11 am
content: Quote from: Mechatrommer on May 30, 2017, 11:16:02 pmI would expect it to display a waveform consistent with a 50 MHz bandwidth limit. The 1 GS/s sample rate is plenty high.What aliasing? And at a 1 GS/s sample rate with a 7ns transition time? The 2465 shows a flat waveform after the last edge and a 50 MHz oscilloscope should have shown the same thing with a 7 nanosecond fall time on the trailing edge. If there was not a problem with the DSO or experimental setup, then I would suspect a problem with the interpolation algorithm, digital frequency/phase compensation, or "bandwidth enhancement".Quote from: joeqsmith on May 30, 2017, 05:19:43 pmI can think of several vintage DSOs like that and I have several of them. I do not usually recommend them because they are less reliable and more difficult to maintain than analog oscilloscopes of the same age simply because of their extra complexity.Do they have any advantages over modern budget DSOs? They can be very inexpensive. Some have full documentation. They usually (always?) make measurements on their processing record unlike several modern instruments and many Rigol models. They often have "retina" level display resolution making up somewhat for lack of index grading.Quote from: tggzzz on May 30, 2017, 08:40:36 pmA low 50MHz bandwidth will conceal any differences between the terminations unless one of them is very broken so comparing them on my 2465 will be more than sufficient. Still, it is something I would check and I often break out my PG506 pulse generator (super clean roughly 500ps rise/fall time) to verify that whatever probe and oscilloscope combination I am using is working correctly.Active probes include more things to go wrong so your x10 HP10020A is probably ideal if its 500 ohm input resistance is acceptable.Quote from: MK14 on May 31, 2017, 01:31:23 amI have a Tektronix 7834 and its write speed is plenty fast to support the needed bandwidth to find glitches and metastability which is exactly what I use it for. It was much less expensive than than a modern DSO of equivalent bandwidth and acquisition rate.Quote from: MK14 on May 30, 2017, 11:39:43 pmWhat is odd is that they have not; they are still produced for the lowest end of the market. Above that they cannot compete simply because of economics even if you ignore the difference in features. It is *cheaper* to produce a DSO because of the specialized non-scalable technology required for high performance analog oscilloscopes while DSOs can take advantage of increasing semiconductor integration.

author: MK14
author_rank: Super Contributor
timestamp: May 31, 2017, 02:30:59 am
content: Quote from: David Hess on May 31, 2017, 01:59:11 amYou are perfectly CORRECT. (I.e. I should have clarified my post above, by saying the historical time periods, when the write speeds were not that good, so needed alternatives, if you needed to see faster signals).What it is (I think), is that at some points in time in history (when these oscilloscopes and similar, were the current state of the art), e.g. 1968 (take the exact time period with a big pinch of salt). The analogue storage scopes (e.g. Tektronix), had somewhat limited write speeds (according to their own documents, if I remember correctly).So because of the limited write speeds, for some applications (probably things like very early TTL 74 logic, and a bit later, very fast ECL logic).Tektronix used alternative techniques (I think it was photomultiplier crt tube technology), to allow engineers to see much higher speed signals.E.g. The Tektronix 485 (if I remember correctly).It was not a storage scope as such, but had ways of getting round it, (persistence of screen phosphor, or similar/something), so that one off events, COULD be seen, even if briefly.I can't remember if it was one-shot or needed repetition to work well.Later (in history), it seems, they produced storage oscilloscopes, which could work at much higher write speeds.Anyway, sorry, if any of the above is a bit wrong. It is because I am trying to remember stuff, and maybe getting it wrong.Quote from: David Hess on May 31, 2017, 01:59:11 amNow you mention it, I remember seeing/hearing about those. They seem to be just for the education (and maybe hobbyist) market. But these are very simple/basic oscilloscopes, which are not really what the OP has in mind, for measuring very high speed pulses etc.

author: 1audio
author_rank: Frequent Contributor
timestamp: May 31, 2017, 03:04:38 am
content: Tek had pretty good storage scopes even in the late 1970's. The faster ones had a mode where the screen "shrunk" to be able to write faster one shot events. And then there was always the camera which used with the special phosphor could capture very fast one off events. Uncle Sam used variations on this for measurements of nuclear tests. In the 1970's and 1980's when I was bringing up new computers and chips the camera and the scope hood were essential. A 4 trace scope and knowing what to trigger it from was all you had but you could make it work with lots of squinting into the dark. And computers like CDC 7600 Cray's and IBM mainframes were pretty fast.With any scope you need to know when its lying to you. With an analog scope the problems are pretty easy in recognize and don't need complex analysis to identify. A DSO has a number of tools to help see complex and difficult phenomena BUT that means many ways to "lie". Not an issue if you know what you are looking at. If you don't (which is the usual reason for getting out a scope) having several different ways to see or not see what you are looking for can lead to mistakes and problems. A lot can be attributed to learning curve. Switching between DSO's makes for complex learning curves, especially when the scope is very complex and time spent looking through menus.A real pet peeve is that today's SOTA scope has a short service life, low resale and are almost unrepairable. Watching a $120K investment become a boat anchor because a motherboard/OS upgrade can't be done is not good (unless you are the manufacturer). Meanwhile my 1990's era Tek 7854 (same class of product) can still do a lot of useful stuff.

author: MK14
author_rank: Super Contributor
timestamp: May 31, 2017, 03:41:27 am
content: Quote from: 1audio on May 31, 2017, 03:04:38 amThat I think, is EXACTLY the part that I was trying to remember.When the writing speed of analogue storage scopes was NOT fast enough. The special phosphor capture + camera, was the preferred method.These days, digital storage scopes, easily capture, even extremely fast, one-off events. Putting such methods (analogue storage and/or using cameras) into the history books.I think the earliest oscilloscopes, were just pens, (rotated with electric motors) paper and electro-magnetic movements. So that the oscilloscope wrote directly the trace, onto paper. Obviously only at extremely low frequencies, then (a very long time ago).https://en.wikipedia.org/wiki/Oscilloscope_history

author: 1audio
author_rank: Frequent Contributor
timestamp: May 31, 2017, 04:01:51 am
content: CRT scopes date back to the 1920's I believe. GR was there pretty early on. Tek pioneered the triggered sweep and the ability to actually measure values from a scope. Before that you used a scope for observing waveform shapes but not much else.The challenge with really fast scopes (20 to 50 GHz) is storing the samples. At those sample rates is not a simple task.

author: David Hess
author_rank: Super Contributor
timestamp: May 31, 2017, 04:13:35 am
content: Quote from: MK14 on May 31, 2017, 02:30:59 amYou got it mostly right but I have detailed notes.First Tektronix used the brute force method of increasing the CRT acceleration voltage which produces a brighter and sharper display with a faster writing rate. People who have not used an oscilloscope like a 485 or 7904 are probably not even aware of this aspect of their performance which applies to both high frequency *and* low repetition rate signals.Next was analog storage CRTs with transfer meshes although I rarely use the transfer mode on my 7834; variable persistence is almost always fast enough for me.Then the 7104 with its microchannel plate image intensifier came out which can produce a single shot mark one eyeball visible trace at a writing ratefaster than the speed of light.1969 7704 150MHz 24kV1972 485 350MHz 21kV Portable1973 7704A 200/250MHz 24kV1973 7904 500MHz 24kV1977 7834 400MHz Reduced Scan Transfer Storage1979 7104 1GHz MCP1987 2467 350MHz MCP

author: MK14
author_rank: Super Contributor
timestamp: May 31, 2017, 04:41:15 am
content: Quote from: 1audio on May 31, 2017, 04:01:51 amThe history, gets complicated.You mentioned the 1920's. Which is potentially perfectly correct, I'm not necessarily disagreeing, here.But I think oscilloscopes (or similar), go back way older than that. But it then becomes more and more debatable, as to what exactly constitutes an "oscilloscope".E.g. if you look at Wireless World from 1911, on the bottom of page 8. It shows an oscilloscope screen, along with its complicated image. I DON'T know specifically how they did it, it may have been some kind of camera, and valve/tube-early-partial-crt phosphor thingy or something.Feel free to take a look (sorry, 1911 was the earliest wireless world I could easily find on the internet).http://69.195.158.203/Archive-Wireless-World/MARCONIGRAPH/Marconigraph-1911-04.pdf

author: ebastler
author_rank: Super Contributor
timestamp: May 31, 2017, 04:53:32 am
content: Quote from: MK14 on May 31, 2017, 04:41:15 amThat picture probably shows a recording from a mirror galvanometer which projects a light beam onto photograpic film, not from a CRT. Such devices were used around that time -- essentially improved, faster chart recorders.

author: MK14
author_rank: Super Contributor
timestamp: May 31, 2017, 04:58:45 am
content: Quote from: ebastler on May 31, 2017, 04:53:32 amSome sources, seem to say that the CRT oscilloscope, comes from 1897, when its crt was also invented.E.g.QuoteSource1:http://theinventors.org/library/inventors/blcathoderaytube.htmI have seen other sources about it was well, on similar lines.E.g.Source2:https://en.wikipedia.org/wiki/Karl_Ferdinand_BraunQuote

author: MK14
author_rank: Super Contributor
timestamp: May 31, 2017, 05:22:56 am
content: Quote from: David Hess on May 31, 2017, 04:13:35 amThat is quite amazing, the "faster than the speed of light", link!It is quite fascinating, reading the history, of how Tektronix, developed their various oscilloscopes, over the years.Their equipment, had a real quality to it, and usually exceptional qualities (for the time period).They were the Rolls Royce or BWM of the oscilloscope world, for a very long time.I also very much admire HP's (who later changed their name) early history as well. But HP oscilloscopes, (in at least my mind), were not up to Tektronix oscilloscopes, in various respects.But much of HP's other stuff was brilliant, for the time, just not so much Oscilloscopes.A bit like Fluke vs Brymen, but maybe that is a bit unfair.I'd probably love to have and play around with one of Tektronix's early valve/tube oscilloscopes, such as the 547. But their horrific size, weight and other impracticalities, FORTUNATELY stop me from getting one. Keeping it working, may also be difficult as well.

author: Fungus
author_rank: Super Contributor
timestamp: May 31, 2017, 08:35:03 am
content: Quote from: Mechatrommer on May 30, 2017, 11:16:02 pmBandwidth issues aside; the first question I'd ask a 'beginner' who showed me that screenshot would be, "Are you using the little spring on the probe?"

author: Mechatrommer
author_rank: Super Contributor
timestamp: May 31, 2017, 12:02:47 pm
content: Quote from: David Hess on May 31, 2017, 01:59:11 am1GSps will sample every 1ns, i'm suspecting risetime is quicker than 7ns (that you saw in the Tektronix 2465, both scopes in the OP is somewhat "BW limited or low passed" during transition). with sub ns risetime added with BW limited acting in the scene, you'd expect only few funny sampled points available for transition representation. granted with poor sinc(x) implementation of the rigol dso, pretty much it can be anything. keep in mind shannon theory, if signal contains freq element higher than 2X sample rate, no digitizer in this world will be able to contruct the original signal correctly.Quote from: David Hess on May 31, 2017, 01:59:11 amlook again closely in the OP pictures (do i need to photoshop to highlight it?), in 2465, there is no ringing after falltime of the 7th peak, otoh in rigol you can see low freq ringing after it (on the low side) that should not be there (about same rate as the data rate), interpolation algorithm cant just simply fabricate that, because those are part of sampled points. with that ringing, we can hypothize that the same ringing occured after the falltime or long period peak (0xFF data?) and got superimposed with the subsequent data (0b10101010101010)... as said this is only hypotesis, the truth is who knows what? to ensure whats really going on, the OP need to do either (1) try to terminate the ringing by changing/improving probing method (the OP managed to probe correctly using 2465 but failed on 1052 which is a missing part mystery) or (2) use higher than 1GSps DSO or higher than 0.45/risetime BW, which is somewhere 450MHz scope, thats bare minimum, for the purpose of greater clarity of signal integrity, he should use 1GHz scope or 10GSps DSO or greater. imho.

author: David Hess
author_rank: Super Contributor
timestamp: May 31, 2017, 12:06:01 pm
content: Quote from: MK14 on May 31, 2017, 05:22:56 amThe HP oscilloscopes I have studied strike me as having better circuit design.QuoteI have a 547 and they are another one of those unique models being the last generation before scan expansion meshes became ubiquitous. (1) So they have an unusually sharp trace without needed a high acceleration voltage and they also have no ghosting from a scan expansion mesh allowing a higher contrast display than later CRTs.There is a story that the Tektronix Grass Valley Group which produced television products returned their 7704s in favor of their obsolete 547s because of this. They could not discern the VITS (vertical interval test signal) on the fuzzier 7704 CRT without using the delayed sweep.Quote from: Fungus on May 31, 2017, 08:35:03 amI considered that but I doubt tggzzz would make that mistake and the rising edge just before the horizontal center shows no sign of this.(1) A scan expansion mesh allows for a shorter CRT and lower voltage CRT amplifier which is important for solid state output stages.

author: Fungus
author_rank: Super Contributor
timestamp: May 31, 2017, 12:23:53 pm
content: Quote from: David Hess on May 31, 2017, 12:06:01 pmThere's clearly something wrong with the probing, the way the wiggly bit gets taller as it progresses is also suspicious.The simple solution is:a) Output five 1's instead of four to see your peaks.b) Don't try to characterize 150MHz signals using a 50MHz 'scope.The 1001 advantages of a DSO over an analog boat anchor don't justify this thread.(even if it weren't a troll, which it is - his refusal to output five 1's demonstrates that)

author: Mechatrommer
author_rank: Super Contributor
timestamp: May 31, 2017, 12:27:25 pm
content: Quote from: David Hess on May 31, 2017, 12:06:01 pmprobably the ringing of the high side got cancelled by the longing ringing of the low side before that? or impedance difference/mismatch between low and high output? who knows? making hard conclusion from limited range measurement is not convincing...

author: Fungus
author_rank: Super Contributor
timestamp: May 31, 2017, 12:29:03 pm
content: Quote from: Mechatrommer on May 31, 2017, 12:27:25 pmThis. The chip isn't driving low/high equally.

author: nctnico
author_rank: Super Contributor
timestamp: May 31, 2017, 12:36:24 pm
content: Quote from: Mechatrommer on May 31, 2017, 12:27:25 pmThe way the signal looks (slow amplitude rise and ringing when the signal goes away) definitely points to something wanting to oscillate so there might be a problem in the probing solution used.

author: David Hess
author_rank: Super Contributor
timestamp: May 31, 2017, 12:46:09 pm
content: Quote from: Mechatrommer on May 31, 2017, 12:02:47 pmIf the analog bandwidth of the Rigil DSO is 50 MHz, then at 1 GS/s I expect about 7 sample point on every edge because the transition time cannot be faster than 7 nanoseconds. And whatever reconstruction filter is being used should place every sample point on the reconstructed trace although we have seen before that Rigol is bad about this and maybe that is related to what we see here.QuoteI was thinking that the burst rate synchronized with distortion produced by the reconstruction filter. That would explain why the initial part of the burst is lower amplitude and low amplitude ringing was produced after the burst but for this to happen, the reconstruction filter would need to be 40 sample points long. Could the reconstruction filter do this while not distorting the longer pulses? Does these low bandwidth Rigol DSOs use a bandwidth enhancement filter?Reconstruction filters which include bandwidth enhancement are common in high bandwidth DSOs but I have never seen one on a 300 MHz or slower DSO. It would be fun to make an amplitude versus frequency plot of this DSO and see if there is excessive ripple and if it has a single pole gaussian response producing a 0.35/risetime bandwidth.Quote from: Mechatrommer on May 31, 2017, 12:27:25 pmUsing an identical probe setup with both oscilloscopes should rule this out which is why I asked for details. If I ran across this behavior, I would check my probe setup and leave everything exactly the same (including the feedthrough termination) while swapping oscilloscopes. The Rigol should be showing a 50 MHz bandwidth limited version of what the 2465 shows. Enabling the 100 MHz bandwidth limit on the 2465 would be informative.

author: Mechatrommer
author_rank: Super Contributor
timestamp: May 31, 2017, 01:20:49 pm
content: Quote from: David Hess on May 31, 2017, 12:46:09 pmpossibly this. freq respond plot of the china DSO is something to be desired. once venturing this subject, is not beginner territory anymore. but we hobbiest loved to use crippled/cheap tools to do stuffs at some level of "confidence"Quote from: David Hess on May 31, 2017, 12:46:09 pmas said, this is something to be desired. i've been wanting to do this since my DS1052E, but to do this we need super duper FG and DSO to verify the measurement. iirc there are some discussing here on fast pulse respond of the Rigol DSO, but that limited to that only, what we need to do is a complete freq sweep from say 10MHz to 200MHz, or preferably up to 1GHz range, but thats not cheap. for example this guy (below) did it with higher end gears (he is a eevblog member? not sure who he is), but sadly its still limited and of questionable validity, ie his measurement setup could be different from us, we say sometime need to measure on a short 50ohm terminated BNC, etc. his test is using standard bundled probe... with the proper respond plot, i believe we can make better measurement through signal recompensation. tedious job yes, but thats an effort if we want to make out something usefull, from something cheap...

author: David Hess
author_rank: Super Contributor
timestamp: May 31, 2017, 01:55:01 pm
content: Quote from: Mechatrommer on May 31, 2017, 01:20:49 pmThe usual tool for this is a leveled sine wave generator or any signal source and a thermal power meter or sampling voltmeter.QuoteA test using a reference level pulse generator is very informative but sometimes not sufficient. Unfortunately as you point out, most of the people buying budget DSOs lack one so reliable test data is rare. The best test I have seen of a DS1000Z which was hacked to 100MHz showed a significant but obscure problem in the transient response which I suspect was caused by slew rate limiting from a stage which was being driven into cutoff or saturation. This distorted the edge and caused a roughly 20 nanosecond recovery time which is exactly what I would expect of a 50MHz design that is pushed to 100MHz.QuoteI am always pleasantly surprised when the oscilloscope's response is practically identical with and without using a high impedance passive probe and I have come to expect this.