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Connection Lost -1073807194



All I have simple VI I am using to Transmit various different messages over a USB COM port (using FTDI chipset) to a device then carry out a subsequent RX.


Some messages do not result in a reply back from my device and in this case I do not experience a problem, however when I use a message (e.g. send a status request) that causes my device to give a reply I get the "Connection for the given session has been lost" error whilst attempting the RX.


My RX is achieved by using a using a VISA get property node to get the no. of received bytes and then feed this to a visa read. It seems the error occurs at the visa read. It seems inconsistent as occasionaly the error is not generated on the first TX & RX cycle, or during the first few.


Although I have read some similar posts on here concerning this there are a few gaps which I need to fill to help me resolve the problem. I am using LV 7.1 on winxp service pack 2.


1) How can I find out my version of VISA as i understand an out of date version could be the problem

2) I have tried the documented trick of using the VISA set I/O buffer size but am usure of what mask value should be used if it is failing on RX


Any help much appreciated.

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Message 1 of 10

I am now using ft245rl chip as the usb controller.I faced a lot of problems wih communication initially.


Please go throught he following stes


  • There will be a function called vcp in the ftdi website.You need to download this to enable serial comminication.(VCP drivers)
  • there will be something called d2xx functions for lv 7.0.You need to download this to enable communication directly through their drivers.
  • First i will suggest you download d2xx function and try their loop back example.
  • Revert back if it works properly.



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Message 2 of 10
Also what is the ftdi chip you are using?
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Message 3 of 10

There is a Knowledge Base article on this error code, but it was for Win-2000.  Don't know if it applies to Win-XP..

The article mentions VISA 2.5 which is a rather old version.  Which VISA version are you using?



Message 4 of 10



I am using the FT232BM.



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Message 5 of 10



Is it neccessary to take the D2xx route to get round this problem? I am using the VCP drivers so that I can treat my device like a virtual com port.


This has worked well for me for ages when I have used the same FTDI device with an RS485 interface,


The only difference here is that I am using an IBIS interface which runs at a slower baud rate and has different data bit/stop/start/parity settings and a different electrical interface, I cants  why this would start generating these errors.


Can anyone inform me how ro acertain what version of VISA i have please.





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Message 6 of 10

Here are a couple of ways to verify which VISA version you have.


(Preferred):  If you have MAX (Measurement & Automation Explorer), simply open the program, expland the "software" tree and look at NI-VISA, the version number should appear in the box on the right.  In my case, I have VISA 4.2.





(not necessarily accurate):  START menu, All Programs, go into National Instruments> VISA > Documentation> NI-VISA Read ME

It will describe which VISA version you have..  Example, I get:


National Instruments NI-VISA™ Software for Windows, Version 4.2

Read Me First, July 2007

© 1995–2007 National Instruments Corporation. All rights reserved.

Message Edited by JoeLabView on 08-29-2008 01:03 PM
Message 7 of 10

Hi ATE Man,


I hope your well.


I am looking into your issue.


Firstly, I would like to repeat the request to know what version of NI-VISA your using, on face value your issue seems to be in the driver layer.


I have been looking on the FTDI website and have found a link for LabVIEW examples (maybe try these incase its your code that is an issue). Also, you will need to use/install FTDI drivers also. 


Please response with an update/more information.



Message Edited by Hillman on 09-01-2008 10:36 AM
Kind Regards
James Hillman
Applications Engineer 2008 to 2009 National Instruments UK & Ireland
Loughborough University UK - 2006 to 2011
Remember Kudos those who help! 😉
Message 8 of 10

 Hi ATE Man,


I was just wondering how things were coming along with your application and I am just posting to check if everything went ok and whether the problem was resolved as I have not heard back from you.  If you have any further questions on this issue, please respond.



Kind Regards
James Hillman
Applications Engineer 2008 to 2009 National Instruments UK & Ireland
Loughborough University UK - 2006 to 2011
Remember Kudos those who help! 😉
Message 9 of 10

I am currently using LabVIEW 2010 and TestStand 4.2 to test a series of UUTs.  The UUTs contain a FTDI FT232R chip to convert a USB bus into a serial COM port.  I am using VISA mapping to connect to the COM port, along with a windows registry edit to 'lock' the COM port locations on the test PC (preventing Windows7 from adding a new COM port for each new UUT tested).  So far, this part works fine.
After each test, I need to disconnect the first UUT then connect the next UUT.  The resource is found and mapped into the appropriate COM port location.  Unfortunately, when I re-run the test, the error message "-1073807194: VISA: (Hex 0xBFFF00A6) The connection for the given session has been lost."  The only way I have been able to continue testing is to exit and restart LabVIEW.  This test needs to be made fully automatic for production line purposes.
Is there a way in LabVIEW to re-acquire the VISA resources without having to exit and restart?  Do I have to use the d2xx drivers to talk to the FTDI chip instead of the VISA drivers?

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Message 10 of 10