32 bit integers transported over gpib

[karl_ender]

Hello,

I am currently writing a controlling and data aquisition software for an Instron testing machine with a GPIB Bus with Labview. The machine isn't the youngest, so I can only use the 488 commands, not the VISA commands. My controlling software works this far, but with the data aquisition I encountered some problems for which I couldn't find a solution this far. I just taught Labview to myself two months ago, so sorry if my questions seem silly to you. I searched the forum and the internet and couldn't find an answer to them.

So here's my problem:

I am Reading out data from my Machine with the command "GPIB-Read", it gives out a string, so I gues it automatically assumes that the data is encoded in ASCII. The machine though uses its own coding, described in its manual! I can read the header of the measurement (it is "#I" in ASCII), after that there is a 32-Bit signed Integer representing the length of my data block. Then there is a 16-Bit Byte and after that many 32-bit signed Bytes that represent my measuring data. There are no seperation marks.

When I read it out, I just get a string of crazy ASCII code (besides the "#I" at the beginning)

My approach to decoding the message this far is this:

I convert the ASCII code to binary code (not with Labview yet, I couldn't find out how it works either. is there an easy way to do this?) , then I ignore the first 64 Bits (2x8Bits of the header+ 32 Bit Integer+16 Bit Integer) and then I try to split up the string in an array of 32 Byte  long strings and see if the data is right. In my measurement, i had three values which where constant, so it should just be three alternating values. I always get wrong data and I am mostly not working with Labview, but I have to later on, because I want to display the data in real time.

It's a lot of work and I just wanted to know, if I'm on the right track or if there is an easier solution. Later on, it shouldn't be a problem to display an integer array as a wave, right? Are there any hints or advice you can give to me?

Sincerely,

Simon

[crossrulz · Accepted solution]

1. VISA calls 488.  So I don't see why you can't use the VISA functions.
2. A Byte is 8 bits.  So there is no such thing as a 16-bit byte.  That is a word.
3. Unflatten From String is your friend here.  You can use it to decode each part of your command.  And since your actual data is just a string of 32-bit words, you can use the Unflatten From String to turn that into an array directly, just make sure the "Data includes array size" is set to false.

[karl_ender]

Thanks a lot for your quick answer! I'll try it out as soon as I get back to the university. Your right, I accidently wrote 32-bit Byte instead of 32-bit Integer on accident a couple of times.

[karl_ender]

I just tried it out and everything worked out perfect 🙂 I've been sitting on this for a while now, but with your help I could programm the whole data aquisition in a couple hours this morning. Thanks again!!

Simon