Communication to DF1 and Modbus

[eward]

I am using Labwindows 7.1 and I am looking to connect to two different devices using RS485. I will have two different 485 ports. One Device is an Allen-Bradley Adjustable Frequency AC Drive(700 series) with a DF1 RS485 Adapter . The other device is a Optitemp Heat Exchanger with a Love Controls Microprocessor (model 16A2) installed (this uses the Modbus as well as a LovelinkII protocol) My question is what is the easiest way to talk to these two protocols (DF1 & Modbus). It seems I have two options: Using Visa or using Datasocket and opening up OPC server/clients(or maybe I have more options?). If I go the OPC route it looks like I would NI Industrial Automation OPC server CD. But my two devices aren't explicitly listed on the NI website as supported. I will only want to do basic functions and queries with these two devices. Visa looks a little more straight forward (using ViWrite & ViRead). OPC looks more complicated but maybe more specific and maybe the driver cd(if compatible) will allow me do things at a higher level. Any help and/ or pointers are greatly appreciated.

Thanks

[ryank]

The problem with using VISA is that you'll have to manually construct the Modbus protocol for your commands (have a look through some of the information at www.modubus.org to get a feel for what this involves). While possible, this isn't a trivial task. While OPC by itself may be slightly more complex than VISA, you'll save a lot of complexity because it implements the Modbus protocol for you.

If you decide to go the VISA route, I wouldn't reccomend starting from scratch. There are a number of libraries and examples out there, both free and commercial for doing Modbus communications with LabVIEW. I'm not personally familiar enough with any of them to recommend one, but I can point you at a couple of possibilities:
One of NI's alliance members has a product called BusVIEW:
http://sine.ni.com/apps/we/niaa.ind_pro_view?p_all_id=4954&p_display_all_id=8929
A couple of similar forum postings with links:
http://forums.ni.com/ni/board/message?board.id=170&message.id=71682&requireLogin=False
http://forums.ni.com/ni/board/message?board.id=170&message.id=78977&requireLogin=False

Hope that helps,
Ryan K.

[cosmo]

Hi
I would strongly encourage the OPC route. I have used CVI 6 & 7 as a gui for an AB ControlLogix system and it worked quite well.

I was talking to an ENBT module in the chassis over Ether/IP using the OEM version of RSLinx on the computer. If you can't find a Rockwell OPC server that supports ModBus, find one from an automation group on the web that you trust. You'll have to see if you give up any functionality by using OPC in your case, but usually you can work it out. Good luck!

Orlan