VISA communication with Serial/USB device

[jtallent]

Hi,
    I'm trying to connect to an industrial wireless modem that responds to the standard AT modem command set.  I've had no trouble whatsoever communicating with this device using Windows HyperTerminal connection; however, when I try to communicate with the device using LabVIEW I continuously get an error when writing to the device (sending commands).  The device is a USB device; however, the manufacturers drivers configure it to be seen as a serial device in Windows.  As a result, I've been using the VISA serial vi's. 

To give a easy example, if I use the example vi "Basic Serial Write and Read.vi" as found in the LabVIEW help, I can open a serial connection using the following settings:

    baud rate:     230400
    data bits:      8
    parity:           NONE
    stop bits:      1.0
    flow control: NONE
    delay:         500 ms

The error is returned when I try to send a basic command to the device.  The returned error is "-1073807298" which occurs at the error out of the "VISA write" vi.  If I monitor the activity at the serial port while running this vi, everything works as expected and I see the connection open; however, when LabVIEW writes to the port the following error is displayed in the port monitor "IRP_MJ_FLUSH_BUFFERS" immediately after the string is sent to the port.

To test the communications more fully, I also looked at the com port/serial device status in MAX and using the same setting, MAX validates that it works correctly.  However, if I open the VISA test panel in MAX, and test the write function in the test panel I get the following error "BFFF003E". 

My only idea is that part of the VISA write vi incorporates a buffer flush that HyperTerminal does not do and this buffer flush is not supported by the device.  If someone can provide even a little insight into a potential problem and how I can go about fixing it, it would be greatly appreciated.  Thank you very much for the help.

-Justin

[pBerg]

Howdy jtallent,

You've got the right idea regarding the flush VISA performs after each read/write call. The KnowledgeBase article here goes into more detailed explanation on the BFFF003E error and provides a technique you can use to prevent this from happening. Another document you may find pertinent discusses how serial communication via Hyperterminal differs from LabVIEW VISA commands: Why Does My Serial Instrument Work In Hyperterminal, but not in LabVIEW or MAX?

[jtallent]

Thanks a ton!  That seemed to do the trick.  Seems so simple now.    Thanks again.