Group UDS wonders

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Smac770

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Hello,

I'm using a HEX-NET 0.4436.4 with VCDS 18.9.1. The car is a 2009 A4 B8 (aka 8K) with 2.0T CAEB motor. So UDS protocol for the engine.

With my HEX-CAN+USB, I could do Group UDS, but was limited to 8 values. Without grouping, I could do 12, but the values for a single cycle were too separated in time. HEX-NET would let me use the Split UDS function, so I got that.

But I see I remain constrained to 12 selections overall. Is that a limitation of the Audi system, or a legacy limitation of the Ross-Tech implementation? Is there a chance this might be lifted at some point? Since Group UDS can do 8 values per shot, I was hoping the split functionality was going to let me split the selections into two groups of 8.

Regarding the Split options, "by 7, 8, 9, 10, 11". If I go 12 selections, then I assume I would split 6+6, or evenly. That's not even an option. Regardless that I can run through each option and see what it does (it appears to be x selections split by y, the first sample group is x-y entries and the second sample group is y entries), what am I missing regarding why those particular options and wording was used?

When using Group UDS, we get results that are same time stamped. What's the feeling about how synchronized those values really are? Is the ECM still processing them in a sequential manner? So they're closer than otherwise, but will never be perfectly aligned?

Thanks,
Scott
 
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Uwe

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Twelve values is indeed a bit of a "legacy" limit dating back to the days of three Measuring Block Groups, each consisting of four items.

The reason the different split options exist is because some control modules will not allow more than 7 items in a request and some will allow more.

When you group UDS requests (and the number of items in that group is below the split value), VCDS sends a single request for all the items in that group and the ECU replies with a single answer. The time at which that answer is received is the basis for the time stamps in the log. We are not privy to how ECU sequences or processes that request internally, so we are unable to say exactly how synchronized they are.

-Uwe-
 
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Smac770

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Thanks for the insight. Engine is the only UDS module in my car, so the 8 per group limit is all that I've known. So I would pick "by 8" under that idea. But we can't go past 12 parameters, so all the by X seems unnecessary. It's either going to be the module can handle 12 at once or you break it into two groups, as every module can handle 6+6 (assumption).

But yeah, it would be really nice if we could bump VCDS to 16 or 20 selectable parameters. By time I pick engine speed, vehicle speed, normed engine load, gear, charge air spec, charge air actual, charge air control spec, intake temp, and term 30, there's not much room left for picking things to try and correlate in my troubleshooting.

Thanks for your time, and for the awesome product. I've been trying to help my uncle use a Foxwell with his Mercedes, ah, the pain.
 
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BB tt

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Twelve values is indeed a bit of a "legacy" limit dating back to the days of three Measuring Block Groups, each consisting of four items.

The reason the different split options exist is because some control modules will not allow more than 7 items in a request and some will allow more.

When you group UDS requests (and the number of items in that group is below the split value), VCDS sends a single request for all the items in that group and the ECU replies with a single answer. The time at which that answer is received is the basis for the time stamps in the log. We are not privy to how ECU sequences or processes that request internally, so we are unable to say exactly how synchronized they are.

-Uwe-

Ok i am confused so same issue if i select more than 8 values it goes to N/A when selecting group uds but what does split do and how do i enable that? I see no split grayed out.

MN07rF6.jpg


s3T9Zf8.jpg
 
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Uwe

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I see no split grayed out.
I'm not sure what's causing that. At first I thought it might be an interaction between the Split control and Turbo! mode (and you are using the latter), but I've not found a way to make that happen here:

CJYHSRQ.png


Can you provide the exact sequence of things you did to get it into that mode?

Try a different sequence. For example set up a split at 8 first thing.

-Uwe-
 
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BB tt

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i selected load from u01 file and then group uds. Will experiment tomorrow. As long as i only select 8 measuring blocks it works, as soon as i add one more it does the N/A. But maybe it is just "switchology", so what specifically does the split do?
 
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Uwe

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Loading a selection from a file is something I hand't tried. But I just did, and I still can't reproduce the grayed-out Split control.

I'm by no means denying what you're reporting, I just can't figure out how to make it happen.

-Uwe-
 
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about to try now, how do i upload a file here and i will attach my u01 file
 
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step 1 select file
Se5WonF.png


step 2 open
I55mCc2.png


step3 check group uds

IGcH6xi.png



step 4 ungroup everything comes back


ptnve9D.png
 
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ohhh just got this

9r67liD.png


so with my hex+can inteface am i limited to 8 measuring blocks for group uds?
 
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Uwe

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so with my hex+can inteface am i limited to 8 measuring blocks for group uds?
It's possible that it doesn't support split. I didn't think of that.

I will try to reproduce it tomorrow. I was doing my testing with a current interface. ;)

-Uwe-
 
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Did you have a chance to test with the hex + can interface?
 
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Uwe

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Just now I did. The HEX+CAN only supports one group. So if you wish to Group UDS requests, you are limited to however many data items a particular control module supports in a single group, but if you don't group them, you can have up to 12.

-Uwe-
 
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So is that a limitation of the dongle hardware or the sw? If you dont group them it makes it very difficult to graph (or in my case damn near impossible)
 
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Uwe

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So is that a limitation of the dongle hardware or the sw?
I expect it's combination. There are features that have been added after the introduction of newer generation interfaces that we can't back-port to the older HEX+CAN interfaces, either because there's literally no room left for adding code in their firmware, or because they have too little RAM to buffer the data.

-Uwe-
 
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Thanks, still worth every penny.
 
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Smac770

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This was the only reason I upgraded my HEX-CAN+USB, because I couldn't log 12 values with Group UDS. Expensive since no upgrade option to just HEX V2, but at least I don't have to cuss at the issue any more.

Uwe, would *really* love if we could get to logging 16 values (two full UDS groups of 8 each) some day.

And my comment way back that the ECU was my only UDS was wrong; turns out the B8 A4 TCM and Airbag are UDS too.
 
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