Products > Test Equipment
SDS1104X-E UART/Serial Decode for 9 bit multidrop/multiprocessor protocol
tautech:
--- Quote from: Raoul Duke on January 10, 2019, 11:19:04 pm ---Thank you everyone for the help. I had moved the trigger level up & down without success. The big issue seems to have been sensitivity to exact timing; once I dropped the baud rate down 1.6%, the decoder has been much more stable. I still wish for a "MARK/SPACE" parity option so that at least I can highlight the address/command words.
From what I can tell, it seems that the decoder is running in S/W after the data capture. Which is nice because it allows for the timing & level changes to be performed on captured data, rather than recapturing it all.
I will now attempt to try the data triggering function, and learn how to make segments work. My current limitation is the 3000 character decode limit. Here's a screenshot of the limit, showing how the analog data identifies two devices by their different driver voltages.
--- End quote ---
--- Quote from: rf-loop on January 10, 2019, 06:47:32 pm ---
It decode rock solid without errors etc. (attached images and just saved "on the fly")
Just set all parameters as they need be and without any problem immediately decode and really rock solid.
then your other message with images
"Here are some screen shots."
With my eyes it looks that there must be some really weird settings. Like something is totally "out of order".
--- End quote ---
I agree, Raoul Duke is still learning to use the X-E to its potential. ;)
@Raoul Duke
For you to have to STOP the scope to get stable Decode you still have some settings to optimize.
All previous screenshots are with the scope in RUN mode and with stable triggering.
Please read previous posts carefully again.
Note, Red boxes in the Decode line indicate errors, you still have some settings to correct.
All we can do if offer screenshots showing correct decoding....unfortunately we do not have your scope in front of us to make the correct settings.
Sometimes it can help to start again after pressing Default to clear any settings that might be corrupting your results.......and yes I was caught by just this showing Decode to member Dubbie one day when he visited. :palm:
Raoul Duke:
The errors are parity errors because I can only pick ODD/EVEN, and the parity bit is being used to identify command/address bytes (mark) from data bytes (space).
The scope is stopped after I fill all 14M of memory with data from power on - 7 seconds of data. I have zero control nor insight into the devices on this bus. They perform auto-discovery after power on and boot. Again, I have zero control over this, because I'm reverse engineering the protocol, not developing the firmware or hardware.
Now that I understand the protocol to some extent, my next project is to make the ftdi_sio driver speak 9-bit multidrop at the oddball bit rate.
Thanks again for the help.
tautech:
Respectfully, without rock solid stable triggering it's hard to get meaningful results.
Your screen captures with a STOPped display indicate the packets are jumping around and trigger settings are not optimum. Trigger holdoff gets it stable for further adjustments to the Decode settings to get a result.
When achieved all the packet boxes all turn blue.
Using Zoom also shows where you are within the data stream.
nctnico:
--- Quote from: tautech on January 11, 2019, 07:22:38 am ---Respectfully, without rock solid stable triggering it's hard to get meaningful results.
Your screen captures with a STOPped display indicate the packets are jumping around and trigger settings are not optimum. Trigger holdoff gets it stable for
--- End quote ---
Read what Raoul wrote: 9 bits is often used in multi-drop protocols using the parity bit as a 9th bit. However the oscilloscope simply doesn't support it and hence the decoding errors when the parity doesn't work out. Now what would be nice is to have a feature which would color the byte based on the 9th bit.
Sorama:
I know this is a rather old topic. But I am running into the same issue, also 9 bit uart with no decent triggering, not even with hold off or a decoder trigger on frame start.
@raoul duke
Did you succeeded in triggering/decoding correctly?
The latest firmware ( at least for the 2000X Plus series) offers a 9 bit as a parity (mark of space’) that is the proper way to decode 9 bit uart.
But even with this setting, I don’t succeed in decoding correctly nor triggering.
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