Need help selecting a logic analyzer  - Page 1
Forum section: electronics / testgear

author: DaveHardy
author_rank: Regular Contributor
timestamp: June 05, 2013, 01:38:20 am
content: I'm a service technician that routinely runs into massive problems in the logic domain. Most of the stuff that I work on is very old and built around the z80 processor with TTL as well as CMOS discrete peripheral logic. These circuits are so old and have so many failure modes that I quite often I need to see the address bus, data bus, and control bus at the same time. I know that there are several fancy scopes out there but I don't have a clue which one I should buy or if I should just go to e-bay and buy a used one.How easy will it be to troubleshoot these circuits with a newer scope logic option?Does anybody have suggestions regarding what I should look at?

author: dfmischler
author_rank: Frequent Contributor
timestamp: June 05, 2013, 01:50:21 am
content: It was more than 20 years ago that I used a Tektronix 1241 for similar purposes, although my job was to make the software work. It was pretty easy to use because there was a ROM pack that could disassemble the instructions and knew how to interpret each bus cycle. These logic analyzers are frequently seen on ebay, but it is often hard to tell how they are configured (because the sellers don't know how to describe what they have), and they usually do not have any acquisition probes. I doubt that they are getting more reliable with age, either.I'm sure a newer logic analyzer design could easily acquire the bus data you need, but I have my doubts that a newer machine will have decode information for such an old CPU. That would mean either you would have to decode the data manually or perhaps do extensive "programming" to make it work well.What is your budget for this equipment?

author: DaveHardy
author_rank: Regular Contributor
timestamp: June 05, 2013, 01:59:48 am
content: If I absolutely have to, I could cough up 3K. I don't really care about manually decoding. I'm more concerned with seeing some logic chip acting wonky and the logic analyzer simply reporting a 1 or 0.Yeah, I'm scared to buy expensive test equipment off of e-bay that is even 10 or 15 years old because there is a good chance that it has been on all day every day since it was bought.I like this but it's really expensive for something that is 15 years old..http://www.ebay.com/itm/Tektronix-TLS-216-Logic-Scope-16-Channel-2GS-s-OPT-13-1F-with-16x-P6240-TLS216-/310666853744?pt=LH_DefaultDomain_0&hash=item48552ffd70

author: dfmischler
author_rank: Frequent Contributor
timestamp: June 05, 2013, 02:11:42 am
content: Nice. But that TLS-216 doesn't really have enough channels to see the address and data bus at the same time, but I'm sure you could do a lot with it if you tried. But checkthis HP 1630Dout. Maybe cheap enough to take a risk? I expect that manuals can be downloaded, etc.Oh,look at this Tek 1241...

author: Rufus
author_rank: Super Contributor
timestamp: June 05, 2013, 02:13:18 am
content: Quote from: DaveHardy on June 05, 2013, 01:38:20 amI don't know of any scopes with more than 16 channels which isn't enough to set up say a full address bus decode trigger and look at anything else at the same time. For old equipment a logic analyser from the same era would seem appropriate and luckily they are not much use any more so go cheap.I would look at what HP/Agilent analysers you can get on ebay and read up on them see if you think they will be useful. Some have the option of a couple of scope channels which will be useful, otherwise check you can get a trigger out and have a scope that can use it.

author: marmad
author_rank: Super Contributor
timestamp: June 05, 2013, 02:17:08 am
content: Quote from: DaveHardy on June 05, 2013, 01:38:20 amDo you have to get an MSO or standalone analyzer?It sounds like you're dealing with clock speeds < 25MHz. You might take a look at theIntronix Logicport; you can download and demo their software. It has 34 channels - and I've used it a couple of times with z80-family processors, while monitoring the full address and data bus plus control lines.

author: Lightages
author_rank: Unknown
timestamp: June 05, 2013, 02:19:22 am
content: With the slow speed stuff you seem to be working on I would buy a PC based USB logic analyzer.http://www.saleae.com/logic16http://www.zeroplus.com.tw/logic-analyzer_en/products.php?pdn=3&pdnex=listhttp://www.pctestinstruments.com/

author: DaveHardy
author_rank: Regular Contributor
timestamp: June 05, 2013, 02:28:00 am
content: I thought about a USB based device but when I checked 6 years ago, everyone said that USB devices were junk. Can they decipher all of the odd ball switching levels in TTL and CMOS with ease? Some of the problems that I will be facing involve stuff that just hangs on the margin, overshoots, noise issues, bleed, etc.I know I'm contradicting myself, but is this a good product and is is possible that I could get by with it?http://www.home.agilent.com/en/pd-1945069-pn-MSOX2012A/oscilloscope-100-mhz-2-channels-plus-8-digital-channels?&cc=US&lc=eng

author: bingo600
author_rank: Super Contributor
timestamp: June 05, 2013, 11:33:36 am
content: The MSO you refer to only has 8 chans ....Didn't you want to look at Addr+Data+Ctrl ?This one has a good reputation (i don't have one) , and i think grabbers are extrahttp://www.pctestinstruments.com/But whatever you get , make sure you get the probes & grabbers with.A used ebay analyzer can be like just 10% of the cost of the "missing probes & grabbers"/Bingo

author: nctnico
author_rank: Super Contributor
timestamp: June 05, 2013, 11:49:40 am
content: Quote from: DaveHardy on June 05, 2013, 01:38:20 amYou could look into a Tektronix TLA704, TLA714 or TLA715. These are PC based logic analysers. Be sure to buy one with probes. They are not very expensive and offer many channels. The software and manuals can be downloaded from Tektronix.Then again I'm not sure whether a logic analyser helps solving your problems. I use an oscilloscope to look for 'strange' logic levels (signal with slow edges or which only go half way) and see whether chip select signals still work. That usually reveals the cullprit within reasonable time.

author: amyk
author_rank: Super Contributor
timestamp: June 05, 2013, 11:54:04 am
content: Quote from: DaveHardy on June 05, 2013, 02:28:00 amThose are analogue issues, and a scope will be much better for troubleshooting those than an LA.

author: dfmischler
author_rank: Frequent Contributor
timestamp: June 05, 2013, 11:54:33 am
content: Quote from: DaveHardy on June 05, 2013, 02:28:00 amYou could probably get by with a four channel scope and a few tricks (that is how most of this stuff was designed in the first place). But that doesn't mean it's the best tradeoff of your time and money.I remember watching a good hardware designer ringing out a new PC board in the early '80s. He had strapped a microprocessor's data bus to a NOP (no operation) instruction (by lifting the data pins and tying them to ground or a pull-up) so that the address bus would count up and read all addresses so he could check all the address decoding logic. I remember thinking that was pretty slick at the time.

author: Fraser
author_rank: Super Contributor
timestamp: June 05, 2013, 07:59:18 pm
content: I purchased a 32 channel Hantek 4032L for around GBP140 and I thought it worth the risk rather than buy an elderly 'boat anchor' or expensive new high end unit. It will meet my needs and may meet yours. It has a sampling rate of 400msps and 2GB of DRAM. The software is not great but it is, IMHO, better then some of the 24msps USB streaming units.I believe in dipping my toe into the water rather than diving in with a large financial commitment.If you don't like the cheaper units you can always sell it on and you will have gained knowledge of the cheaper units limitation in your specific scenario.There are pictures of the 4032L internal parts in another post of mine on this forum.

author: Pinkus
author_rank: Frequent Contributor
timestamp: June 05, 2013, 10:27:26 pm
content: Quote from: bingo600 on June 05, 2013, 11:33:36 amI have one. Very good software. I could solve everything in the past with it. Highly recommended by me!Peter

author: codeboy2k
author_rank: Super Contributor
timestamp: June 05, 2013, 11:29:23 pm
content: Quote from: PeterK13 on June 05, 2013, 10:27:26 pmI have one.. very good trigger modes and good software, never crashes. Its pretty fast too, has state and timing modes.. Only downside is the lack of memory but they have a compression option so this helps. I find that you have to have good triggers to capture what you want, there's not enough memory to blindly capture everything and just start hunting through the capture.

author: Evit
author_rank: Newbie
timestamp: July 02, 2013, 12:32:30 am
content: I'm not an expert, but this is a good readhttp://www.janatek.co.nz/janatekdesign_faq

author: profmason
author_rank: Contributor
timestamp: July 02, 2013, 07:14:38 am
content: I have a hp 1631d that I got a lot of use out of in the late 90s and early 21st century, but bought a usb logic analyzer a few years ago and haven't looked back. The hp was a $10k instrument in 85 or so which would be like a $50k instrument now. All the protocol analyzes on the usb instruments make them much more useful. Plus they fit easily in your laptop bag.