Logic analyzer newbie question - Page 1
Forum section: electronics / beginners

author: dav
author_rank: Regular Contributor
timestamp: May 21, 2016, 09:55:29 pm
content: Hi all,let's say I would study the communication between a CPU and memory (old CPUs, like Z80 and so on).Could I put the logic analyzer probes on the data bus (8 bit) and view the data as bytes? (not bits)I know each channel of the analyzer will show a bus data line (so D0,D1...), but would see the data grouped as bytes (D0,D1,...,D7) in hex.

author: alank2
author_rank: Super Contributor
timestamp: May 21, 2016, 10:03:00 pm
content: Yes, you will need a logic analyzer that can group the bits and show you the byte value. Most of them will do this. You will want one with a lot of channels!

author: danadak
author_rank: Super Contributor
timestamp: May 21, 2016, 11:05:35 pm
content: If you want to get started with a logic analyzer on the cheap thisis an example of one on ebay. Although only 8 channels which meansyou cannot look at a byte wide buss triggered properly, althoughyou could sample it it manually. Or use 2 to get up to 14 bits and 2control bits.You download Saelae software to run it.https://www.saleae.com/downloadsRegards, Dana.

author: dav
author_rank: Regular Contributor
timestamp: May 22, 2016, 07:39:57 am
content: Thanks for reply.Obviously I don't want to see consecutive 8 bits of same channel grouped in byte, but one bit per each channel (all sampled the same time) grouped in byte.What's the right name of this "function"?Is this 16 channel LA good for me?Zeroplus LAP-C16032http://www.zeroplus.com.tw/logic-analyzer_en/products_info01.php#tab-2ndThanks

author: danadak
author_rank: Super Contributor
timestamp: May 22, 2016, 09:45:16 am
content: I am not familiar with this vendor, but obviously look around webfor comments on the model to see if there is any serious drawbacksto the unit.Regards, Dana.

author: alank2
author_rank: Super Contributor
timestamp: May 22, 2016, 02:06:13 pm
content: If you need a lot of channels, you might want to look at the Intronix LogicPort. It can handle 34 channels at 500 Mhz and can combine multiple channels into a single value like you are looking for. Sometimes you can get them on eBay for less if you are patient.If you get one of the 8 channel 24 Mhz cheap clones from eBay take note that I've seen some webpages that show them to use the wrong input buffer - one that is only 3.3V tolerant. 5V will cause it to be out of spec and sink 7mA.

author: dav
author_rank: Regular Contributor
timestamp: May 22, 2016, 08:10:45 pm
content: Again thanks to all.I took a look to Intronix LogicPort; it's a lot out of budget for me (price $389).Nobody knows if the Zeroplus LAP-C16032 can combine multiple channels into a single value?I ask for this model due to its reasonable price (about $100)

author: Kjelt
author_rank: Super Contributor
timestamp: May 22, 2016, 09:34:36 pm
content: Yes the zeroplus can do this.Download the manual and take a look at section 4.2They call a set of grouped signals, a bus.You can display a bus and also trigger on it (if it reaches a certain value for instance)

author: rstofer
author_rank: Super Contributor
timestamp: May 22, 2016, 09:50:15 pm
content: One thing to be aware of is that the ZeroPlus unit linked above, indeed the entire series, can only have one level of triggering according to the spec sheet here:http://microcontrollershop.com/product_info.php?products_id=3369That's kind of a big deal when you want to trigger on some event that happens after another event that happens after some first event. Multiple levels of triggering may be required more often in state analysis.It would be worth reviewing the documentation or even installing the software just to see what they mean by '1 Level'. I know what I think it means and it isn't helpful (for me).