Serial bus decoding not as expected

Posted Sun, 19 Mar 2023 21:49:45 GMT by Mishrikey, Matthew Devel Engineer

Hello,  I am using an MDO4054B-6 with firmware 3.22 (latest available I believe), with DPO4BND module which includes serial bus analyzer.   When I decode a 1553 stream, it identifies the Sync, and the RT Address, however the remainder of the command word or status word is just 11 bits that are not decoded, grouped, or tagged in any manner, followed by the parity bit.   In a YouTube tutorial video published by Tektronix, I can see the decoder (using MSO4104B) should also be able to identify the transmit/receive bit, subaddress, and word count. Not sure but maybe it can also identify Mode Code. So I gathered a few screenshots of what I am seeing on my scope, and also some of the YouTube video.  Is there some software update I need to make to get the decoding to be more useful like in the video?   Thanks

Posted Tue, 21 Mar 2023 18:42:23 GMT by Teles, Afonso

Hi Matthew, The decoding seems to be working as expected until it reaches the receive/transmit bit, suggesting the waveform data doesn't match what the instrument expects for the 1553 protocol. I would ask that you post here a waveform file of one of these waveforms that are giving you trouble so I can further help you with this problem.

Posted Wed, 22 Mar 2023 00:45:59 GMT by Mishrikey, Matthew Devel Engineer

Thanks Afonso.  I am attaching following: 1) Screenshot of a captured BC-RT command alone.  The command being sent by my BC is 04-1-16-01 (RT address 4, Transmit, Subaddress 16, one data word). In hex that is 0x2601.   2) Screen shot of corresponding Event Table, which correctly shows payload 0x2601. 3) Waveform file (ISF) for the one waveform.  I think there is not a way on the scope to save the corresponding bus signal or event list other than the screenshot.  But if there is a way I can try.

Posted Tue, 28 Mar 2023 18:07:11 GMT by Teles, Afonso

Hi Matthew, I apologize for the delay. I tried the waveform on one of our MSO4000B's and got the same decoding. Next I tried it on an MSO5 and I got it to decode properly, but only with maximum response time (RT) set to 4.1 us or lower (screenshot attached). I tried setting the maximum RT to below 4.1 us on the MSO4000B but was not able to successfully decode the bus. Further work is needed to understand this issue. I would suggest changing changing the time/div and RT maximum and minimum and seeing how that affects the decoding, it might be possible to make progress that way.

Posted Tue, 28 Mar 2023 18:38:44 GMT by Mishrikey, Matthew Devel Engineer

I tried it with a little more data (RT response with one data word).   If I play with the RT max/min, sometimes I get correct decoding on the RT status word only.   The BC command never gets decoded no matter what the setting. I played with time/div, amplitude, bus thresholds, and trigger position. Screenshot attached, as well as the additional data.   I'm trying to understand if this is a bug in the decoder, or if the signal is bad in some way.  Because you said it works fine on MSO5, it makes me think it is the former.

Posted Tue, 28 Mar 2023 23:02:05 GMT by Teles, Afonso

I wouldn't say it works fine on the MSO5. Yes, I can get it to decode somewhat closer to what you expected but it still throws a sync error at the end. This leads me to believe the waveform itself is somehow misshapen (I don't know enough about 1553 to say how exactly) and the MSO5 simply has a slightly different decoding procedure which I have abused to force it to decode something else. I have attached screenshots with the bus decode table to show that. It would be useful to know the minimum and maximum RT of the measured system.