Writing Binary in VISA LabVIEW (

[Psquared]

If you are familiar with C#, this might be easier to understand where I'm coming from.  In C#, I would use this function to put together a blob of binary data to write to VISA:

IMessageBasedSession.FormattedIO.Write();

That particular method can take strings, arrays of bytes, etc.  To my knowledge I can find no equivalent in the VISA VIs available in LabVIEW.  I think the VISA write VI provided automatically writes and flushes the buffer, so I would need to build the entirety of what I am sending into one data structure, then send it on its way.  It only accepts a string, so I thought to convert the bytes to string - didn't work.

[SOUR1:DATA:ARB1 HALFSINE_POS, ] - then from there append the array of bytes.  In C#, I would write a string to the buffer, then write the bytes to the buffer (as bytes), then flush and everything worked.  I'm seeing no option to do that here - am I missing something?

[GerdW]

Hi P²,

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@Psquared wrote:

[SOUR1:DATA:ARB1 HALFSINE_POS, ] - then from there append the array of bytes.  In C#, I would write a string to the buffer, then write the bytes to the buffer (as bytes), then flush and everything worked.  I'm seeing no option to do that here - am I missing something?

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A string is the same as an array of bytes, and there are two functions to convert between them (StringToU8Array, U8ArrayToString).

What have you tried and where are you stuck?

[Kyle97330]

You say you "so I thought to convert the bytes to string - didn't work".... how did you do the conversion?  Was it this?:

https://www.ni.com/docs/en-US/bundle/labview-api-ref/page/functions/byte-array-to-string.html

That is exactly how I have sent binary data over VISA before and it has worked.

Perhaps there's something else involved?  You don't say what device you're writing to so I can't look up the protocol, but perhaps you need to prepend a message length, or add a null termination character, or something else along those lines.

[Psquared]

I am talking to a Keysight 33622A Function Generator.  Everything I am trying to do in LabVIEW I have already done in C#, so I know that it is possible.  The unsigned byte array to string conversion was one of the efforts I had made, but since you've said you have made it work I will have to take a look at the string as a whole when I get back to it in the morning.  It sounds like I might be on the right track; I'm hoping it is something simple.

[Psquared]

@GerdW

Tried:

Type cast (Byte Array -> String)

Flatten to String

Byte Array to String

What I do is write the command, then concatenate the Byte array -> String conversion and then call the VISA write VI.  The instrument doesn't like any of the above.  

[Kyle97330 · Accepted solution]

It's almost certainly in IEEE-488.2 binary block format, then.

So, in addition to your binary data you need to send a # sign, then the length of the length, then the actual length, and only then add your binary in.

Plus also making sure that the byte order is correct...

[billko]

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@Psquared wrote:

I am talking to a Keysight 33622A Function Generator.  Everything I am trying to do in LabVIEW I have already done in C#, so I know that it is possible.  The unsigned byte array to string conversion was one of the efforts I had made, but since you've said you have made it work I will have to take a look at the string as a whole when I get back to it in the morning.  It sounds like I might be on the right track; I'm hoping it is something simple.

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It is simple.  Not quite a no-brainer, but the advice given is sound so you should be able to work out the details with no problem.

[Psquared]

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@Kyle97330 wrote:

It's almost certainly in IEEE-488.2 binary block format, then.

So, in addition to your binary data you need to send a # sign, then the length of the length, then the actual length, and only then add your binary in.

Plus also making sure that the byte order is correct...

This.

I realize now what was going on.  I remember debugging a similar issue in C#, except that then I coded the BinBlock format into the string and for "some" reason I saw the #3456 on the write buffer to the device.  Turned out that the WriteBinary method in C# automatically coded BinBlock into the write.  That's not the case here in LabVIEW, since don't have that option - building that BinBlock string and adding that in did the job.  I buried that functionality into the abstraction of my classes once it got working in C#.  Another interesting thing I came across is that I had to swap the "endian" of my float -> bytes conversion in C# and didn't have to do that here.

Simple things indeed.  But a good learning experience.  Thanks for the guidance.