which oscilloscope?

lly, we

We have a few very high end LeCroys for deep memories and a bunch of low end Tek's for everyday work, but they really skip on memory, for some reason they charge $1000's more for a decent size memory, no one here likes the Agilent's

Good idea. Thanks. If my highest-frequency digital signal is 25 MHz, do you think a 100 MHz digital scope is sufficient? What is a digital-learning scope?

Please do not top-post. You have lost all connection with the previous articles. Your answer belongs after (or intermixed with) the quoted material to which you reply, after snipping all irrelevant material. See the following links:

(taming google)

I'd see if you can find a 100msps+ Analog, with 200Msps+ Digital (5ns), that should be at the 'bottom end', as that's quite do-able with mainstream FPGA and ADC parts.

The Digital Model can also be a PC based one (it's all pixels), whilst the analog model, clearly is not.

As an example, this is one I use :

-jg

For serial protocols a logic analyser will be much for useful, and have a

The analyser will either sample the (digital) waveform with an internal or external clock, much like a scope, or, more usefully only timestamp the waveform transitions. This allows best use to be made of the devices memory.

Yes.

John

Ca you recommend a manufacturer of PC based logic analyzers ? (surely I can do a search, but it is better to hear from a person who knows.)

Personally I almost exclusively do FPGA design and the company I work for has the cash to supply professional analysers. Currently I use an Agilent

You really need to look at your memory depth (bearing in mind the analyser only needs to record edge locations in the digital domain), sample rate (generally not a problem if you synchronise the sampling with your system clock via an external clock input), and finally the number of channels you need to observe. From what you say 8 channels would be more than sufficient, which is really the bottom end of LSA capabilities.

Have a look at:-

You really need to decide your requirements, but from what you have said so far you need to spend nothing like the $7000 you were quoting.

HTH

Icky

I was trying to find one test equipment unit that will do everything I need. Now I am leaning more towards an analog oscilloscope, to watch my analog signals, and a PC based logic analyzer. I looked at the links you gave me. That is very good. Thanks.

To throw a different tack on the subject: what probes do you use?

When trying to find glitches, faulty wave shapes and such in fast cpu busses, I find the probes being the bottle neck rather than the scope BW.

I found myself creating probes based on e.g.

...allowing me to see things on a lowly 100 MHz scope that would not be revealed on any high grade scope with (good quality) 1/10 or 1/1 probes.

SW sequence related issues are usually solved by clever (written by SW engineers, not by me :-) SW routines and debug ports. (never needed a logic analyser).

If everything is OK, but the system stops for no reason, the scope + appropriate probe comes out. YMMV - so far I get away with it :-)

For regular digital/embedded stuff, on a 100 MHz scope, any probe will work. When the fuzzies start to matter, a good fet probe is magical.

The way-out extremes are the Tek SD-14 sampling probe, 3 GHz bandwidth and something like 0.3 pF at the tip. And the HP 54006A passive probe,

Me neither. The best logic analyzer is in your head; re-read the source code.

Last week I had a first-article product where the uP wouldn't run code. Two hours of frustration condensed into one sentence: one of the data lines must be pulled down by \RESET to tell it to boot in 8-bit mode, and the schottky diode that does that had a bad solder joint, and probing the most handy node, the diode lead, fixed the problem temporarily, and the diode is *under* the eprom.

John

I disagree. The human mind is a terrible bottleneck! ;-)

I've spent many unproductive hours debugging, I should know. (But it's those five highly productive minutes at the end that really matter...)

Tim

You could check out Rigol or Insteck. I think that they are the underlying manufacturers for Agilent and Tektronix.

Depends on the hardware on hand, I have found (not the easy way, I might add :-), that the act of putting a std probe on a wayward adress / data line, changes the conditions enough to make the measurement invalid. Sometimes the fault does not occur with the probe in place (which in it self tells you something), sometimes the device stops working completely.

Or all seems OK. But when the probe is removed, the system crashes after 5 minutes..

I had good results with the 1K resistive low cap probe, showing artefacts

"Talal Itani" wrote in news:t317k.112$cv5.70@trnddc01:

Bring in a sales rep to demo different lines. Tek might not be the best choice, but it is safe, in that when it breaks, nobody can say "Why didn't you buy a Tek?" The warranty is pretty good, too.

For that, your best tool is a protocol analyzer. If you want to use a hardware-based protocol analyzer, consider renting one until your project is up and running.

As an alternative, there are software protocol analyzers all over the net. Google, and you'll find more than you need.

Good luck!

Tom

You can buy used ones pretty cheap, might even be cheaper than renting:

FWIW, if you're going the used route, my all-time favorite protocol analyzer is just about anything from the HP4951 family. Very capable, small and light as those things went back in the day, and simple to use. Suitable for both field and engineering use.

Tom

But a logic analyzer is not a scope. It is pretty rare that I need this sort of buffer for an analog waveform. It is a trade off between features you actually need and ones that you will use once in a blue moon.

In fact, I don't feel the need for a 4 input scope anymore. But what I do want is a scope that can work with a logic analyzer. It has been awhile, but I seem to recall analog scopes that have a trigger output on the back which can be used to trigger other devices.

My customer buys PC attached devices. He is very happy with their Intronix logic analyzer. But they have a PC attached scope that he was having trouble figuring out the triggering. I might ask to borrow the scope and see if I can make it work for me.

Rick