Double word HEX number in ASCII string problem

[Lucky--Luka]

Hi everyone
I need to make a VI that receives 4-byte hexadecimal values as ASCII strings from a CAN-USB interface. I am using an Arduino CAN schield with a firmware that I have not personally written and that I still haven't access to. I do have a problem with the format in which I receive the values. To get the exact value I should add 0 in the middle of the values when missing.
I give an example to explain better.
I get the string:
2 8 D5 0 0 0 0 B 5 70 <CR><LF> (value: 46448)
I'd like to interpret it as:
2 8 D5 0 0 0 0 B 05 70 <CR><LF> (value: 722288)
I'll give another example.
I get the string:
2 8 D5 0 0 0 0 B 4 5 <CR><LF> (value: 2885)
I'd like to interpret it as:
2 8 D5 0 0 0 0 B 04 05 <CR><LF> (value: 721925)
The maximum value I can read in this case is 1000000 in any case.

After I have added the zeros where needed in order to have always groups of two characters I can make something as in the attached VI to get the number that I am looking for.
Does anyone have an idea what algorithm I can use? Thank you!

ASCII-HEX.vi

[Lipko]

The problem is not clear to me. You want to parse the string or do something else with it? Why wouldn't a simple scan from string work? Or do you want to forward the message? How fast should it be?

[ShaunR]

12 hours ago, Lucky--Luka said:

To get the exact value I should add 0 in the middle of the values when missing

I don't think so.

12 hours ago, Lucky--Luka said:

4-byte hexadecimal values

12 hours ago, Lucky--Luka said:

2 8 D5 0 0 0 0 B 5 70 <CR><LF> (value: 46448)

this should be (byte) grouped as

28 D5 00 00 B5 70

that's 6 bytes. I expect the last 4 bytes are the value so the first two (28 D5) are some sort of header. 00 00 B5 70 = 46448 so that seems reasonable.

So. doing the same for your arbitrary insert...

12 hours ago, Lucky--Luka said:

2 8 D5 0 0 0 0 B 05 70

28 D5 00 00 (but what about the B?) 05 70.

since 722288 = 00 0B 05 70 we have [with our arbitrary insert]

28 D5 00 00 0B 05 70.

But that means we how have 7 bytes and have a 3 byte header instead of 2.

Adding a 0 arbitrarily is not the solution here. You need to look at how you (the human) are understanding the data from the Arduino again.

[hooovahh]

More information is needed.  Is this a response to an ISO 15765 request?  UDS, KWP2000, etc.  Or is this periodically broadcasted frames?  If it is UDS or something similar you'll need a CDD file to define how it should interpret the response.  If it is a periodic message then a DBC file will define the structure of the data being sent, and what IDs belong to what data.  I cover the Signal API and how bits can be interpreted in Part 5 of my CAN blog, and I talk about multi frame messaging in Part 8.  If you are trying to reverse the CAN bus without this information, then I suspect you will have a very difficult time.  There is an IEEE Float Data Type in the XNet Database editor which uses 4 bytes so it is possible this will do what you want.  I'd make a database using the XNet Database editor specifying where in the frame the bits are and try using the conversion API with it.

EDIT: Also I think Shaun is incorrect. 

2 8 D5 0 0 0 0 B 5 70

I'm unsure what the 2 means but 8 means there are 8 bytes to read and the 8 bytes are D5 00 00 00 00 0B 05 70.  8 bytes is a common payload length for CAN.

Double Edit: What are your expected values? I ran them through the IEEE conversion and tried Big/Little Endian but ended up with really large numbers both negative and positive.

[Rolf Kalbermatter]

On 6/5/2023 at 11:18 PM, Lucky--Luka said:

Hi everyone
I need to make a VI that receives 4-byte hexadecimal values as ASCII strings from a CAN-USB interface. I am using an Arduino CAN schield with a firmware that I have not personally written and that I still haven't access to. I do have a problem with the format in which I receive the values. To get the exact value I should add 0 in the middle of the values when missing.
I give an example to explain better.
I get the string:
2 8 D5 0 0 0 0 B 5 70 <CR><LF> (value: 46448)
I'd like to interpret it as:
2 8 D5 0 0 0 0 B 05 70 <CR><LF> (value: 722288)
I'll give another example.
I get the string:
2 8 D5 0 0 0 0 B 4 5 <CR><LF> (value: 2885)
I'd like to interpret it as:
2 8 D5 0 0 0 0 B 04 05 <CR><LF> (value: 721925)
The maximum value I can read in this case is 1000000 in any case.

After I have added the zeros where needed in order to have always groups of two characters I can make something as in the attached VI to get the number that I am looking for.
Does anyone have an idea what algorithm I can use? Thank you!

ASCII-HEX.vi 6.73 kB · 2 downloads

Posted on the dark side too and answered there quite extensively. https://forums.ni.com/t5/LabVIEW/Double-word-hex-string-to-number-format-problem/m-p/4309006