What is the relative importance of sampling rate versus sample memory in a digital oscilloscope?
I'm looking at two candidates: one has a sampling rate of 2GS/sec, but only 2.5K of sample memory, while the other samples at only 400MS/sec, but has 1M of sample memory.
For debugging microcontroller systems with typical peripherals (I2C, SPI, ADC, LCD), which is more important, sampling rate or sample memory size?
For your stated purpose, I'd say that a better candidate would be a logic analyzer. Whereas PC-based, USB-interfaced o'scopes tend to be a bit underpowered, similar logic analyzers are often cost effective and a good fit for a home/hobby lab. Hit Google for "usb logic analyzer" for a long list of candidates. My personal favorite (which gets a lot of use developing professional products as well) is the Intronix logic analyzer from
For o'scopes, I'd recommend that you also look at the digital scopes from Instek, which are pretty well thought of around here (I don't have one but I am looking for an excuse...). One source is over at
-- Rich Webb Norfolk, VA
A logic analyzer cannot easily detect marginal line conditions such as overshoots, reflections, marginal levels, bus contentions. I'd go with a scope.
Yep, got a GDS-2204, happy with it. Bought it via Newark because they had the best price:
Yesterday I had to work with one of those TI lunchbox-size scopes at a client. Oh man, what a step back after being used to the Instek. Especially when I hit the 2.5K brick wall at the end of its memory bank where the Instek got 25K.
-- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
Joerg wrote in news:Qtnpk.17924 $ snipped-for-privacy@nlpi064.nbdc.sbc.com:
I had to instrument a whole lab class. I was looking long and hard at Instek, and if it were for my personal use, that's what I would have went with. That said, because they (I ordered 18) will serve multiple people and multiple classes, I went with Tektronix -- I didn't want to hear "Why didn't you go with Tek" the first time one broke.
I did go w/ Instek for everything else-- bench power supplies, bench DMMs, bench function generators. I'm very happy with the power supplies, and actually prefer them to topwards because they have a button that disables output. I'm a tad concerned about the function gens, but they are a whole bunch cheaper than Tektronix, and will be less painful to replace when students blow up the output stages.
-- Scott Reverse name to reply
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Is the 2.5K buffer on the Tek large enough to look at protocols such as I2C and SPI?
For the price differential, you could have just bought a handful of spares and still been well ahead monetarily.
On the other hand, if you ask nicely, Tek might be willing to donate or subsidize equipment for schools -- Oregon State University (Tektronix is in Beaverton, Oregon) had almost all of their undergraduate labs outfitted with Tek equipment through such means. (And guess what? OSU has an undergraduate "robotics" program named... TekBots!)
Tek of course makes lots of really great equipment, but when it comes down to bog-standard low-end equipment that Tek themselves is just re-badging from some Chinese supplier, I don't feel as though I'm getting my money's worth any more.
---Joel
Like a lot of things: It depends. In this case, it depends on what you want to see when you "look at" them. You can certainly grab several characters and check that your voltage levels and slew rates are okay. That's a good and useful thing. It's even possible to do some counting of 1s and 0s on the screen (try to avoid fingerprints) and decode a few characters. Been there, done that, and it gets old really quickly -- especially when the characters are in a continuous stream.
-- Rich Webb Norfolk, VA
IMHO it's not enough. I had the "pleasure" to do SPI debug at a client and all they had was a TDS-220. We had glitches in 64-bit packets and it was a bear to eyeball small timing aberrations. The Instek GDS-2204 does that with ease.
BTW I won't see responses from gmail until someone else answered and quoted you. Best would be to use some better domain.
And _don't_ use a pen, probe tip, screwdriver or any of that either ;-)
There is a classic movie about a loner type guy who becomes a math genius, can decipher all kinds of codes just by looking at the screen and then goes completely crazy ...
-- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
I'd second that.
Logic analysers are handy tools, but NOT as good a scope. You can't beat seeing the true probed digital signal instead of a 0/1 that the logic analyser thinks it sees.
Dave.
It's usable, but often not enough in my experience.
Dave.
Logic analysers are more for the "next level up" where you're confident that electrically all the signals are OK and you're debugging some complex protocol on some big bus. Many people never do anything complex (or buggy?) enough to need one... and perhaps ironically, the need for general purpose logic analyzers is decreasing as large multi-drop parallel busses have fallen out of favor to lots of high-speed point-to-point serial busses all flowing into switch/routing ICs.
"Joel Koltner" wrote in news:tMnqk.28768$ snipped-for-privacy@en-nntp-08.dc.easynews.com:
Let's just say there was very liberal educational pricing. You pretty much start with a pretty good discounted price, and on top of that, one in four scopes is free. I did spend some time trying to track down the right person at Tek for a better deal, and couldn't find that person.
-- Scott Reverse name to reply
No arguments here; o'scopes are necessary tools. On the other hand if the threshold is set correctly then the 0/1 that the logic analyzer thinks that it sees is the same 0/1 that the other digital devices think that *they* see, and that can be a useful thing to see.
-- Rich Webb Norfolk, VA
Yep. I have to turn mine on regularly just to replenish its backup battery. It even went from the bench to a storage area.
-- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
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