Parallel bus decoding on Hameg HMO Scopes - Page 1
Forum section: electronics / projects

author: opticpow
author_rank: Contributor
timestamp: October 20, 2012, 06:32:07 am
content: One for the fellow HMO owners....I have a HMO724 with the 8 bit logic probe and I want to decode a 8bit parallel clocked bus (the data bus on a Z80), and I'm wondering if it is possible to use one of the analog channels for the clock? I seem to be only able to select the POD channels, and they are obviously all busy with the data.Thanks,Wayne.

author: atsthng
author_rank: Contributor
timestamp: October 20, 2012, 03:02:22 pm
content: I would like to know this too... It is possible to trigger the logic pod channels (using the logic trigger) using one of the analogue channels 1-4, but I have not found how to do a synchronous parallel decode with the parallel bus (does not seem to be possible, only asynchronous decoding)...

author: KedasProbe
author_rank: Frequent Contributor
timestamp: November 01, 2012, 03:26:58 pm
content: QuoteI was also wondering if the AUX trigger input couldn't be configured as 1 logic channel....

author: opticpow
author_rank: Contributor
timestamp: November 10, 2012, 10:36:40 am
content: As I could not find an answer to this question, I logged a case with Hameg. Looks like at the moment, the answer is noDear Mr IngramThank you for your request.Up to now you can only decode an 8-bit parallel clocked bus with a HO3508 logic probe that is specified as follows: 6-bit for data, 1-bit for clock and 1-bit for CS.Nevertheless I have forwarded your query to our R&D department which is now considering to use the two idle analoge channels for clock and chip select purposes.

author: KedasProbe
author_rank: Frequent Contributor
timestamp: November 11, 2012, 06:35:02 pm
content: At least support is consistent

author: 0xdeadbeef
author_rank: Super Contributor
timestamp: November 11, 2012, 08:24:44 pm
content: As a side note, on the 4ch scopes, the trigger input can't be used for CS while this is possible on the 2ch scopes. Not a big issue, but somewhat surprising that 4ch scopes lack features of the 2ch ones.About support: the next update is said to be released in the 1st quarter of 2013. I hope it fixes/improves several issues I reported in the last months. Unfortunately, they also rejected/ignored some issues and as the R&D guys typically ignore all answers to their initial replies, it sometimes feels a bit like they don't want to discuss issues and suggestions at all.

author: KedasProbe
author_rank: Frequent Contributor
timestamp: November 12, 2012, 10:39:20 am
content: Quote from: 0xdeadbeef on November 11, 2012, 08:24:44 pmAre you sure, which bus? I don't see it on my 2ch.

author: 0xdeadbeef
author_rank: Super Contributor
timestamp: November 12, 2012, 10:53:50 am
content: CS for SPI. Indeed else the HOO11 option wouldn't make much sense on the 2ch scopes.http://www.hameg.com/datasheets.0.html?&no_cache=1&L=1&tx_hmdownloads_pi1=download&tx_hmdownloads_pi1=5141Then again, the above datasheet doesn't differentiate between 2ch and 4ch scopes, so for the 4ch scopes, the information is clearly wrong.

author: KedasProbe
author_rank: Frequent Contributor
timestamp: November 12, 2012, 11:35:04 am
content: Ah, I (still) don't have the software option, If I would buy my scope now I would for sure use this promotionhttp://blog.hameg.com/?p=70I did ask the local office recently if they could make a promotion price for the HOO10 though.I may not get it since I bought it via conrad and not from the local sales office.Seems If you buy from Hameg you should really do it at the end of the yearEdit:I don't understand why they would not add a dual use for the trigger input for all scopes to be used as logic channel, even without logic probe you would have an extra channel.

author: 0xdeadbeef
author_rank: Super Contributor
timestamp: November 12, 2012, 11:51:25 am
content: Talking of protocol decoders, IMHO the I2C decoding is not implemented optimally, as it seems to be based on clock edges while the protocol defines e.g. that the data can't change in the high period. Which means that the ideal point for sampling data is amidst the high period. Hardware implementations of I2C tend to change the data exactly after the clock goes low and the HMO decoder doesn't like this. If the sample rate is not high enough to have two separate samples for the clock going low and the data line changing its level, it marks the bit as faulty. This means you need amuchhigher sample rate to decode I2C with an HMO scope than you would normally need. E.g. >20MS/s to decode a 400kHz signal. My cheap ZeroPlus logic analyzer can easily decode the same signal with 1 or 2MS/s.Unfortunately, the R&D guy didn't seem to share my concerns about this. Or to be more exact, as I reported issues with I2C decoding of a perfectly valid I2C signal, he sent me an (outdated) I2C spec and claimed "my" I2C timing was too critical. However, this was the hardware I2C of an NXP µC and after all NXP is Philips and Philips invented the I2C bus. Besides, the spec doesn't define any timing between falling clock edge and data edge as it just expects the data to be sampled within the clock high phase, not at the falling edge.Yet, as mentioned before, my answer to his mail was ignored. So it's hard to tell if they at least are aware of that issue internally.

author: kripton2035
author_rank: Super Contributor
timestamp: November 12, 2012, 12:00:57 pm
content: yep this promotion is *really* nice ...Quote

author: KedasProbe
author_rank: Frequent Contributor
timestamp: November 12, 2012, 12:16:27 pm
content: Quote from: 0xdeadbeef on November 12, 2012, 11:51:25 amIf I set a timebase to 20µs/div (8 clock periods) it uses 25MSa/s so that wouldn't be a problem, but yes it is cutting it close and updating the firmware wouldn't be a bad idea.

author: opticpow
author_rank: Contributor
timestamp: November 12, 2012, 02:30:00 pm
content: Quote from: kripton2035 on November 12, 2012, 12:00:57 pmKinda sux that I had to pay for those features myself....

author: opticpow
author_rank: Contributor
timestamp: November 12, 2012, 02:31:50 pm
content: Quote from: KedasProbe on November 11, 2012, 06:35:02 pmI kinda see it as false advertising. They state that it can decode 8bit bus, but when it is clocked (which busses aren't??) 8 bit really means 6 bit data.....Devil is in the details

author: kripton2035
author_rank: Super Contributor
timestamp: November 12, 2012, 04:33:35 pm
content: so you need to buy the 2x8=16 bits version of the scope which is quite a lot more expensive ...and then you really have 8 bits of visible data. thanks hameg.

author: KedasProbe
author_rank: Frequent Contributor
timestamp: November 12, 2012, 04:57:30 pm
content: Quote from: opticpow on November 12, 2012, 02:31:50 pmThe sheet says parallel 4 bit source (obviously for serial there is no problem)But I don't see any reason for them not to fully implement the analog channels as logic channels, it's clearly already on the to do list (if they aren't already busy), otherwise they wouldn't have provided this possible (future) solution.(obviously if they encoder some trouble they may have to cancel it, so they can't tell you for sure they will add it)

author: 0xdeadbeef
author_rank: Super Contributor
timestamp: November 12, 2012, 05:39:13 pm
content: I think you can't combine the digital and analog channels for any protocol on the HMOs. My understanding is that for one decoder, they all have to be either digital or analog. It sounds like a limitation easy to overcome, but then again you never know how complicated this is on the FPGA level.