Can I monitor the VISA read as the data comes in?

[moonrocks]

Hi.
I'm reading the serial data using VISA read.
But I can only see the data when it is finished
reading. This can take up to 5 minutes or more.
Is there a way to see the data as it comes in?
Or atleast see the first 16 bytes of the data?

Thanks,
Van

[Dennis_Knutson]

You can use two VISA reads. Set the first one for 16 bytes and the second one for the remainder of the data. Another way is to put the VISA Read in a loop. Divide the expected byte count by some number and execute the loop a fixed number of times or until there is no more data to be read. Take the output and wire it to an concantanate string function that's wired to a shift register.

[moonrocks]

Thank you Dennis.
I will try that.

Van

[moonrocks]

Hi Dennis,

I have the Read.vi read one byte at a time.
Now I need to concatenate all these characters
into one string. I'm having problem following
your suggestion. Could you verify this?

Thank you,
Van

[Dennis_Knutson]

You should be using a shift register to concantenate the bytes read. Attached is a simple read inside a while loop with the shift register.

[moonrocks]

Thank you Dennis, again.
I'll try this.

Much Appreciated,
Van

[H2Oyeah]

I am having a simular problem.  I am reading the data from the commands that I am writing but the read cannot seem to keep up with the write.  What I mean by this is that I will write a move command followed by a tell position command.  I have these in the same write command box.  I will get some of the position data but it seem to lag behind the write commands as it does not display the correct positon.  I am moving a microscope stage and it is moving correctly and at the end I can use a different visa write and read to check it's positon.  I will include the vi.  Would concentrating the strings like in the pic help?  I was also thinking of puting the two commands in a stacked sequence but I do not know if that will work with the multiple writes and reads I am doing in the for loop.  Thanks for any help.

[Dennis_Knutson]

You have some dataflow problems and I think you have some timing issues. For one, you are using the Wait (ms) and because that function does not have an error in/error out connection, you don't know exactly when the wait is happening. Alos, immediately after you do a write, you check to see how many bytes are available and read that number. It's certainly possible that you are missing some information because the instrument hasn't yet transmitted the information yet. You might want to use a wait function after the write, then check number of bytes, and then do the read. Use the Time Delay function which does have error in/error out so that you can enforce dataflow with resorting to sequence structures. Sequence structures are not something you should use a lot of. You can also put a loop after the write and do a Bytes at Serial Port and exit the loop when the byte count is equal or greater to a certain number.

[H2Oyeah]

Thanks for the help I will post if it works.

[H2Oyeah]

That did the job very well thanks very much.