RS485 Transceiver Mode setting resets after closing VISA session

[bdybala]

I have a PXIe-8431/8 that I am trying to use in 2-wire Auto mode on all ports.  I know I can change this setting from the default 4-wire in MAX when running as Administrator, as well as with Device Manager.  However, I would like to do this programatically (my serial communication is implemented using the .NET SerialPort class, but I can use C++ or TestStand to change this setting if needed).  I've tried using DeviceIoControl as well as viSetAttribute.  In both cases, if I read the setting back after writing it, it is correct (RS485_MODE_2W_AUTO (3)).  If I close the CreateFile() handle or the VISA session I used to change the setting and then open a new session or handle, reading the Transceiver Mode attribute returns the default of 0 (RS485_MODE_4WIRE).  I have tried running my code as Administrator with the same results.

Since the transceiver mode can be changed in MAX or Device Manager, I know this setting can be persisted across multiple sessions.  How do I save this setting across multiple sessions programatically?

Thanks,

Brandon

[MauraW]

Hi bdybala, 

You can change the transceiver wire mode on Ports for National Instruments Serial Boards programatically by following this article: 

http://digital.ni.com/public.nsf/allkb/1D516C10D7EDFAC6862571110073B8F4 

Is this what you were looking for? 

Thanks!

[bdybala]

Maura,

I have already implemented the calls to setViAttribute and getViAttribute as shown in the LabWindows/CVI example you linked to.  However, this only works for the duration of the current until the first call to viClose().  If I create a new instrument session (a second call to viOpen()), the result of a new call viGetAttribute() shows the original transceiver mode setting, not the value that I previously set.  I've modified your linked example below to illustrate the issue.  I have tried running my code as Administrator, but the problem remains.

#include <ansi_c.h>
#include <visa.h>
#include <cvirte.h>

static ViInt16 RetWireMode;
static ViSession RSCHANDLE;
static ViSession INSTHANDLE;

int main (int argc, char *argv[])
{
    if (InitCVIRTE (0, argv, 0) == 0)
        return -1;    /* out of memory */
    
    
    viOpenDefaultRM (&RSCHANDLE);
    
    viOpen (RSCHANDLE, "ASRL3::INSTR", VI_NULL, VI_NULL, &INSTHANDLE);
    
    viGetAttribute (INSTHANDLE, VI_ATTR_ASRL_WIRE_MODE, &RetWireMode);
    printf("Original Wire Mode %d\n",RetWireMode);
    
    // Default value is VI_ASRL_WIRE_485_4WIRE, so change a 2-wire auto.
    viSetAttribute (INSTHANDLE, VI_ATTR_ASRL_WIRE_MODE,
                    VI_ASRL_WIRE_485_2W_AUTO);
                                                    
    // RetWireMode is VI_ASRL_WIRE_485_2W_AUTO
    viGetAttribute (INSTHANDLE, VI_ATTR_ASRL_WIRE_MODE, &RetWireMode);
    printf("New Wire Mode %d\n",RetWireMode);
                                
    viClose (INSTHANDLE);
    
    // Open a second instrument session
    viOpen (RSCHANDLE, "ASRL3::INSTR", VI_NULL, VI_NULL, &INSTHANDLE);
    
    // RetWireMode SHOULD be VI_ASRL_WIRE_485_2W_AUTO, but INSTEAD is
    // the default VI_ASRL_WIRE_485_4WIRE (as if the call to viSetAttribute()
    // above had no effect).
    viGetAttribute (INSTHANDLE, VI_ATTR_ASRL_WIRE_MODE, &RetWireMode);
    printf("New Wire Mode %d\n",RetWireMode);
                                
    viClose (INSTHANDLE);
    
    getchar();
    
    return 0;
}

Thanks,

Brandon

[bdybala]

Does anyone have any other suggestions?