The Deditec USB-Logi-250 LA - what the forum say ? - Page 1
Forum section: electronics / testgear

author: roli_bark
author_rank: Regular Contributor
timestamp: June 08, 2013, 07:38:39 am
content: http://www.deditec.de/en/logikanalysatoren/prod/usb-logi-250.htmlQuite an impressive spec of features (36 Ch., 250Msp/s per Ch., 0.5M Samples memory depth per Ch.). Around € 600. At least on paper it looks like a fantastic choice. What does the forum say ?

author: roli_bark
author_rank: Regular Contributor
timestamp: June 08, 2013, 09:37:58 am
content: Some more detailed data from Spec:Number of Channels 36x (TTL level with 2,5V / 3.3V / 5V are possible)Inputvoltage: 0V to 5VLevel:Low: < 0.8VHigh: > 2VSample buffer 512Kx36 BitTimingmode, Sampling Frequency 250 MSamples/sec down to100 samples/sec (internal clock)Statemode, sampling rate from 0 to 100 MHz (external clock signal is delivered by a target)===What I notice is that the Timing mode 250M sampling is a somewhat limiting factor for sampling data above 25Mhz, and for catching hazards (glitches) detection.

author: marmad
author_rank: Super Contributor
timestamp: June 09, 2013, 03:10:33 pm
content: The hardware looks good - although the software (I downloaded and tried quickly) doesn't seem to allow you to run it in Demo mode - which is a pity.Quote from: roli_bark on June 08, 2013, 09:37:58 amDigital sampling specs are not the same as analog sampling: the inverse of the sampling rate (in this case, 250MSa/s = 4ns) will likely be the edge (peak) detect - and probably 1/2 the rate will be equivalent to the pulse detect (i.e. 125MHz maximum; 8ns).Quote from: mojo-chan on June 09, 2013, 01:25:27 pmHow the software looks is irrelevant - although how it operates would be good to know. And the interpreters are easy to find in the documentation: SPI, RS-232/RS-485, CAN, I2CQuoteThis is wrong - since it disregards sample compression (even forgetting about timing versus state analysis). Having used both the Saleae Logic (with it's 'infinite' buffer but maximum 24MHz rate limited to timing mode) and the Intronix LogicPort (with 2k sample buffer with compression but 500MHz  / 200MHz  sampling rates), I can say without a doubt that the LogicPort is WAY more useful.

author: roli_bark
author_rank: Regular Contributor
timestamp: June 16, 2013, 11:00:29 am
content: Thanks for the enlightments.Indeed, the Intronix LogicPort looks like an impressive contender, except its very limited samples memory. Be it compressed or not, it seems to quite impossible trace long records - seconds - at higher sampling clock rates.Is there a way to overcome?Sent from my GT-I9300 using Tapatalk 2

author: roli_bark
author_rank: Regular Contributor
timestamp: June 26, 2013, 12:30:50 pm
content: Quote from: marmad on June 09, 2013, 03:10:33 pmCan some elaborate on the "buffer with compression" ?Does that mean that theoretically more than 2K samples buffer depth can be stored ?If yes, how many samples actually ?Thanks

author: marmad
author_rank: Super Contributor
timestamp: June 26, 2013, 12:37:05 pm
content: Quote from: roli_bark on June 26, 2013, 12:30:50 pmIt depends on how often the signal is changing. Since digital signals only have two states, simple run-length encoding can be used. For example, if a signal goes high for 100 clock cycles (which would be 100 samples without compression), you just store the number 100 in a single byte. So in this case, compression is 100:1.

author: roli_bark
author_rank: Regular Contributor
timestamp: June 27, 2013, 06:21:41 am
content: I see.Is the so called "compression" effective per channel ?If so, it is basically the same as a VCD capture method used in storing waveforms in Tabular form.VCD isn't exactly a "compression" (that increases Entropy alike *.zip), but rather a "Print-On-Change".In my experience, storing waveforms in VCD format, reduces file size by a factor of 10(on the average, for a typical digital stimuli/response scenario).If this is a representative case, then most probably it yields an effective 20K capture buffer/channel for the Intronix.

author: free_electron
author_rank: Super Contributor
timestamp: June 27, 2013, 09:08:04 am
content: Quote from: marmad on June 09, 2013, 03:10:33 pmHow the software looks is the most important factor ! ( im not talking about color scemes here but about how you can visualise the captured data )All these cheapo boxes , in fact almost any logic analyser out there even super expensive ones, capture a lump of 1's and 0's . The power of the machine is determined by the visualisation capabilities !Bus decoders, signal groupin ginto busses , packet decoding , state decoding and state tracking, tabular display,mnemonic display , source display (through linking via an OMF file) even being able to display a group of signals as an analog wave.Being able to visualise the same lump of data in multiple ways simultaneously ( through an MDI or multiwindowed interface ) being able to open multiple vieports at different timestamps so you dont have to scroll all the time.That is where real machines excel.I am going to restate what i just wrote in the other logic streamer (which is what this thing is. I won't call it an analyzer as those capabilites are very weak) topic.These thingies are good to look at an i2c signal . Thats it. Hook em up to a real feature like a pci bus amd they will cause errors instead of letting you find errors.Oh we do 250mhz.. Sure.. Over those crummy testleads ? What about programmable trigger levels.?Oh we are compatible with 2.5 3.3 and 5 volt..Really ? Let me translate that . You basically have an fpga or cpld in there, running at 3.3 volt with a series resistance so you can overload it with 5 volt signals. The pin level selection is set to 3.3 volt ttl. Meaning anything above 1.7 volt is seen as logic high. So ther. You slap on 'it works with 2.5 volt to 5 volt logic'.A real logic analyser has per-pin trigger levels. You can set hresholds for high and low independently. If a runt pulse comes through that does not meet Vihmin or Vilmax it will be rejected . Doing this will let you see the real digital pattern as perceived by the real application.These thing are toys. They are useful for some very simple work. Try anything real (like seeing a pci bus transaction , which is only 66MHz) and they will fail miserably. They fail as hardware because of the way they are designed, they will fail,as test instrument as they will be the cause of errors, and they willl fail at software level because you will have to look at a bunch of waves. The machine cannot be fed a state table and flag errors for you. (Which is what real analysers can do)Here is a simple test on how weak these things are. i will take something from the hobbyworldAn i2c bus. two wires, 400khz. very simple.low speed and running at 5 volts levels.Try to set up the analyser to do the following : trigger if 'no acknowledge' is detected on i2c.Any 'no acknowledge' is fine. I'm not asking to filter on address or anything. Simply : hey analyser , if you see a failed acknowledge : trigger and show me the captured waveform (let's do 50/50 pretrigger and post trigger so i can see what happened before and after.)Good luck... If it can't even do something simple like that it can't be called an analyzer.I'm not asking to do bus decoding even (thats visualisation which is a whole other can of worms). Simply trigger if no ack is detected.I am almost 100% certain all these boxes will fail the test.They have no sequence triggering. To do this you need to be able to tell the machine.If scl=1 and sda = falling then start sequenceSequence:Count 8 falling on sclIf sda=0 -> trigger else : idleThis is a really basic example as all the stupid mixed signal oscilloscopes with a bus decoder can trigger on such a simple thing... If you 'logic analyser' can't then what good is it ?Like is aid. These things are simple grabbers for 1 and 0 made by people who have never seen nor used a real logic analyzer .

author: marmad
author_rank: Super Contributor
timestamp: June 27, 2013, 09:30:12 am
content: Quote from: free_electron on June 27, 2013, 09:08:04 amHow something "looks" refers to the visual appearance of something - How something "works" refers to what you're writing about.QuoteThis is easily done on the Logicport. It depends on the device and the software; whether it can be done on this device would require DLing and testing (or fully examining) the software. Making a blanket statement about all LAs is fruitless.

author: free_electron
author_rank: Super Contributor
timestamp: June 27, 2013, 11:14:23 am
content: Quote from: marmad on June 27, 2013, 09:30:12 amThe logicport is different. I'm talking salae, usbee and all the other 'streamers'.But also thelogicport will have tremendous limits compared to a real analyser. It may have some additional logic for a number of common, simple things, but it won't be fully programmable.The triggering capabilities of a real analyser are very impressive. They essentially have a sort of custom cpu that runs in lockstep with the sampling and evaluates the stream as it is flying by. Tha requires a serious lump of ligic. That cou executes a mini program that you can write as user.

author: marmad
author_rank: Super Contributor
timestamp: June 27, 2013, 11:20:32 am
content: Quote from: free_electron on June 27, 2013, 11:14:23 amBut you responded to my comment - which was specifically written to do exactly that: point out the difference between the Salae and the Logicport. Plus you're commenting in a thread asking about a device which seems (based on a quick look at the capabilities and software) quite similar to the Logicport.

author: roli_bark
author_rank: Regular Contributor
timestamp: June 27, 2013, 06:49:16 pm
content: free_electron,Sure, you want a 'real' analyzer? Pay!Get yourself one of these $40k & above LA's.This thread, and basically all this forum, is about hobbies equ.Sent from my GT-I9300 using Tapatalk 2

author: nctnico
author_rank: Super Contributor
timestamp: June 27, 2013, 09:54:03 pm
content: Fortunately there a lots of pros hanging around here. A professional logic analyser can be bought for little money from Ebay. The down side is that these need a serious investment of time to learn how to use all the advanced features. And even the modern ones are boat anchors.I have a high end LA from Tektronix with about all the bells and whistles one could wish for. In most cases I just capture a trace and look for the problem. I have used the advanced trigger capabilities only a few times. Another feature I like to use is the statistics view which shows how much time was spend in a certain state. Very handy for profiling software with minimal intrusion.IMHO the small logic analysers like the one this and the other thread are about are sufficient for 99.9% of the problems you'll ever need a logic analyser for. You can forget about measuring SATA, PCI express, USB, etc interfaces. The probes alone cost a fortune and the chips which meet the specs should just work. If you doubt the signal path impedances you can use a spectrum analyser (reflected power) or use TDR.

author: free_electron
author_rank: Super Contributor
timestamp: June 27, 2013, 09:55:27 pm
content: @roli bark : no need . I have 2. A 16702b with 272 channels at 4 gigasamples/s and a 36 channel pattern generator. And a 16900a with another 132 channels. They cost me about 400$ each ...It wouldnt really be that hard to put in some advanced triggering. A small cpld can do the work.The brunt of the work is the software part on the pc side.

author: roli_bark
author_rank: Regular Contributor
timestamp: June 28, 2013, 07:49:09 am
content: Quote from: free_electron on June 27, 2013, 09:55:27 pmI envy you. How did you get these for just $400 ?Quote from: free_electron on June 27, 2013, 09:55:27 pmI guess you're right.I also don't see a VERY nice feature of "Transitional Timing mode" on the other plain vanilla USB LA's.See here for details (on The GoLogic LA which has it):http://www.nci-usa.com/frame_features_software.htmBasically what it is, is that it adds the capability of sampling (clock) based on a channel transition.This isn't trivial to implement as it sounds.

author: free_electron
author_rank: Super Contributor
timestamp: June 28, 2013, 12:31:07 pm
content: Quote from: roli_bark on June 28, 2013, 07:49:09 amWhat you describe is clockless state mode. My machines can do that. They look at the input. If one line changes they store a sample and slap a timestamp on it. The sample depth on the board halves in that mode. But you can do extreme long recordings. One word holds the sample the other the timestamp. Since one channel is 68 bits... You can have looooong times between samples.As for how i got those. One on ebay, the other local. The ebay one was listed 1 day only, local pickup. I initially lost the bid. I got a call in the afternoon (after bid closed) that there was only one other dude and he had looked over local pickup only. This was a company that made hardware at one point but now sells the ip block. They were moving , the junk in the old lab had to go. The receptionist was tasked with clearing out the building. Any money collected was going towards buying a new printer scanner fax , or other things to enliven the new office. The stuff had to go as they had to turn in the keys that night. If nobody bought it it would end up in the trash. I got that one for 300$. Fully loaded with 4 acquisition boards. The machine ,when empty (without acquisition boards) was like 28000$. One acquisition board is over 30000$. These boards are huge. Full with memory , huge xilinx fpga's , 4 custom chips with big heatsinks on em and a ton of channel interface chips.The second on i bought at a local company yardsale. It was a lump deal. There was a microohm meter, a power supply a frequency counter and the analyser. All were defective. I paid like 480$ for all of it. All the equipment is already repaired. The analyser problem was that it would not boot correctly. It would boot but you could not log in to the LA default account.I simply requested the recovery disks from agilent , reimaged the drive and now it works correctly.That machine has only one acquisition card in it. The acquisition boards from the first one are compatible i just need a different mounting bracket. When i merge the machines i will sell off the old one on ebay for a few hundred $ . The target is to cancel out what i spent so they are essentially free.I had an even older one that i bought for 200$, but i already sold that one on to the next happy user.

author: roli_bark
author_rank: Regular Contributor
timestamp: June 28, 2013, 07:56:30 pm
content: Amazing story.Quick calc: in its hay days (late 90's?) the 1st one + 4 Acq. Boards worth close to $150k....