rs485 2-wire using DSC IO server

[kinnikinnick]

Can anybody tell me whether it is possible to use the DSC module to create a Modbus IO server using RS-485 in 2-wire mode? 

I'm using a cRIO controller with the NI 9871 module in scan mode, and I can successfully communicate with my Modbus slave device (Omron 3G3MX2 variable frequency drive (VFD)) using the MODBUS Library for LabVIEW (see link here: http://zone.ni.com/devzone/cda/epd/p/id/4756).  But my understanding is that the DSC module is made for situations like this - to talk with industrial equipment such as a fairly common VFD, many of which use 2-wire RS485.  

By the way, the DSC module is working great in the same project, running a RS232 Modbus IO server. 

Marvin, CLAD

[Kareem_W.]

Hi Marvin,

It appears that this is indeed supported. Please see the link below:

Modbus RTU RS485 Labview 8 DSC:

http://forums.ni.com/t5/LabVIEW/Modbus-RTU-RS485-Labview-8-DSC/m-p/430760?requireLogin=False

Regards,

Kareem W.

[LV_Tim]

I have the exactly same issue.

Did you get this to go?

[kinnikinnick]

Hello LV_Tim,

No, I never got MODBUS to work with an IO Server (via DSC module) over RS485 2-wire.  I ended up using the Modbus Library found here:   

http://zone.ni.com/devzone/cda/epd/p/id/4756

Regards,

Marvin, CLAD

[Matthew-B]

Hi everyone,

We have done some further investigation on using the NI 9871 with Modbus I/O Servers. You can use the NI 9871 with Modbus I/O servers, but it is unfortunately not possible to configure the wire mode of the NI 9871 port.

There is one workaround that we've developed which uses either the LabVIEW Modbus API or the Modbus API that ships as part of the LabVIEW 2014 DSC Module. You can create a Modbus Serial master/slave using a VISA resource name but should set the wire mode prior to creating the Modbus master/slave:

Best Regards,