Use NI-VISA control Ethernet communication with VNA

[xinli]

My VB code doesn’t show any error message but my PC to test equipment (VNA) Ethernet connection just doesn’t work. I use OpenChoice Instrument Manager from Tektronix to monitor IP connection and it detected VNA's IP . But the value my VBA code reading back from VNA buffer (variable feedbk as in below commands ) is always empty. I expect to see “100 connections accepted” as shown in OpenChoice . My code is stat = viOpenDefaultRM(defaultRM) stat = viOpen(defaultRM, "TCPIP::10.85.148.61::5000::SOCKET", VI_NULL, 20000, sesn) ( after above line executed, stat=0 which I think means viOpen is success) stat = viSetAttribute(sesn, VI_ATTR_TMO_VALUE, 15000) feedbk = Space(80) status ("Waiting for VNA connection") stat = viBufRead(sesn, feedbk, Len(feedbk), Actual_Length) ( I expect the readback value in feedbk is “100 connections accepted” but it is always 0) Any suggestions is appreciated

[Chris V]

Hi xinli,

I was looking at the documentation for this function and it's a little confusing.  However, I think you need to pass a pointer to your feedback string, instead of the feedback string itself.

Have a great day,

Chris

[xinli]

Chris,

Thanks for the reply.

Would you please give an example how to pass pointer to string?

Regards

Xin

[Chris V]

Hi Xin,

Check out this article for pointers in VB:  http://www.codeproject.com/KB/vbscript/how_to_do_pointers_in_visual_basic.aspx?df=100&forumid=1232&e...

Also, what is the value of your stat variable after the viBufRead() ?

Most devices must have a command sent out over TCP/IP before they will return information.  Is this not true for your device?

Have a great day,

Chris 

[xinli]

Thanks, Chris

I will double check what "stat" is after viBufRead() . I rememer it is a negative number.

This code works before even it is not stable. Once a while is no connection and I need to restart my PC or VNA and finally it will connect. But now it look really dead.

On my PC I have TekVisa and NI-VISA (Tekvisa to control Tektronix equipment and NI-VISA for VNA). A few days ago I ran my VBA code for VNA testing, my code complains some functions not defined. I think when I updated TekVISA a few days ago,  TekVISA replaces some dll files from NI_VISA (for example VISA32.dll). Then I install latest NIVISA again (5.0.3), hope to recover my code.

After I add VISA library to my VB code, I got this error message

" VI_NULL : constant expression required" in below command

 stat = viOpen(defaultRM, "TCPIP::xx.xx.xxx.xx::5000::SOCKET", VI_NULL, VI_NULL, sesn)

Then I input visa32.bas and the error message is gone. I think install of  NI-VISA may put it somewhere than VBA project expects.  Now my Ethernet connection is really dead.

Regards

[xinli]

Chris,

The "stat" values are as

1) stat = viOpenDefaultRM(defaultRM)

    stat=0      defaultRM=58317368

2)  stat = viOpen(defaultRM, "TCPIP::10.85.148.61::5000::SOCKET", VI_NULL, 20000, sesn)

      stat=0      defaultRM=58317368   sesn=58302528

3) stat = viBufRead(sesn, feedbk, Len(feedbk), Actual_Length)

    stat= -1073707339   feedbk="                ..."

 ( I expect the readback value in feedbk is “100 connections accepted”)

According to the equipment programming document, it has no command sent out over TCP/IP before return information.

Thanks

[Chris V]

Hi Xin,

Is your stat variable a string?  From looking at the documentation, it looks like that functions should be returning a string.  What you've posted looks like you are representing it as a number.

Have a great day,

Chris

[xinli]

Chris,

I define "stat" as Vistatus. " feedbk" is string so I expect see readback string in variable "feedbk"

stat = viBufRead(sesn, feedbk, Len(feedbk), Actual_Length)

Thanks

Xin

[Chris V]

Hi Xin,

As I said before, the documentation here is a little fuzzy.  I'm working with R&D right now to find out exactly what that error code means.  I'll get back to you as soon as I hear something.

Have a great day,

Chris

[xinli]

Chris,

Thanks for the help.

I checked online for similar problem and found one may help us. You can google it "Problems with the tekvisa_dll in instrument". Their solution is to change equipment IP address. I will give a try and let you know. 

Regards

Xin