How to change parameter(wavelength) of serial port instrument in Labview?

[RavensFan · Accepted solution]

Don't branch your VISA wire.  Go through Write, Read, Write, Read.     Let the wires determine your data flow.  When you split your wire either Write would happen in parallel, then either Read, it was hit or miss where the response wound up.

[ProTon4ik]

Thank you for your help. The program is working properly, I can do what I wanted, and now I am just improving program for my uses.

Do you know why those 2 elements on screenshot don't work? I want to define start point of parameter  before loop with using them, and then to change that parameter in the loop.

[RavensFan]

A picture of the block diagram doesn't show me what you have entered into that string control.

And Bytes at Port is the wrong thing to use 99.9% of that time.  If what you do in the loop works, then it will work outside of the loop as long as you are doing it the same way.

I recommend you read Crossrulz's presentation from earlier this year about serial communications that tries to clarify the mistakes people do, including the mistakes that NI has in their serial example VI's.

VIWeek 2020/Proper way to communicate over serial