convert a hex string to bytes/values

[nitad54448]

Hi

Sorry for what it seems a basic question (I am an amateur in bytes and stuff).

I read some info from an instrument through a TCP Visa connection. Data is read either as Ascii or Bin as follows

To distinguish between ASCII command and binary data from the instrument each data block is transmitted in the following format:
0 1 2 3 4…Len+4
TypeHi TypeLo LenHi LenLo Data
LenHi, LenLo contain length of the Data part of the message, TypeHi, TypeLo determine the type:
• TypeHi = 55h, TypeLo = AAh – ASCII command, Data part of the message contains the ASCII string
(transferred string is not terminated by CR!).
• TypeHi = 66h, TypeLo = BBh – binary command, Data part of the message contains the binary
stream data.

I have difficulties in reading these. an exemple of what I tryin (without success) is attached here (not of much use but it gives an exemple of what the instrumet sends back).

Thanks for help

[altenbach]

Looks like the numbers are formatted as comma delimited decimal integers in the string, not flat binary. What values do you expect for your example string?

[nitad54448]

The string received should be something like PRESNC:-412,-412 but includes a header marker like "55AA" for a ASCII and two bytes stating the length of the string submitted.

[nitad54448]

In the doc I have this, but as I am noob, I don't know how to handle it :

[crossrulz · Accepted solution]

What you should do is read 4 bytes.  You can use the Unflatten From String to get the data type and the data length from those 4 bytes.  You then read the number of bytes stated in the data length.  You can then parse the data based on the data type.

[altenbach]

Start with something like this (you can easily add more cases, one for each header type):

1. See if the first 2 bytes are x55AA (Add cases for all other possibilities)
2. unflatten 2 bytes to get the length of the message
3. Clip the remaining string at length (not needed?)
4. Scan two values as SGL, assuming a format of "PRESNC:%f,%f" You can easily cut the substring to the ":" and treat the remaining string depending on what it is.
5. If there could be a variable amount if comma separated values, you could use spreadsheet string to array (not shown).

[nitad54448]

Hi

Thanks, can you post it as LV 2020 or below ? (sirry, I am not up to date !)

regards

[altenbach · Accepted solution]

Here's my version of Tim's above. I definitely would not make 55AA the default case, of course.

As I mentioned:

• if the "PRESNC:" header can vary, use another case structure.
• If the number of values can vary, create an array instead of a cluster (using spreadsheet string to array" with comma as delimiter).
• ...

[nitad54448]

Hi

thanks, it works. I just wonder how to read the other possibility with the 66BB in which the number of values is variable (I can not make a "variable" cluster...). anyway, thanks, I will try to figure it out.

Another problem I have : how to mark 2 solutions in this forum ?

regards

[altenbach]

• If the number of values is variable, use a 1D array instead of a cluster.
• If you want help with the 66BB situation, feel free to attach a typical received raw string for that option.
• What is the dataype of the "binary stream data"??? (SGL array? I16 array? Byte order? etc.)
• I think you can mark more than one solution.