I was wondering if those that have experience with  Modbus devices, would like to give their 2 cents on the difference, advantage, disadvantage of the different modbus devices. Why would someone choose one over another, price , easier for setup, etc...
I think it would be quite helpful to the newbees to modbus hardware.

Brg,
  Richard Konnen

So what, nobody wants to give their opinions on the different hardware?

Hello rkonnen:

I just noticed this thread tonight, and will give some feedback.
There are several kinds of Modbus devices available, and as far as I know, they all work.
Perhaps the most common usage for Modbus is installing a potentiometers for Feedrate override, and Spindle override.

My first Modbus device used was the Cubloc brand. If you check out their website, they have a wide variety of boards. Programming the board is done with the CuBasic program, which is able to monitor and debug your program logic. Cubloc uses Ladder Logic, and/or Basic. They are the only ones to use a combination of Ladder and Basic, which run simultaneously. After your program is working, it becomes a stand-alone board, connected <> the serial port. If your computer does not have a serial port, you can use a serial converter that makes a USB port a virtual serial port. Cubloc has an excellent manual, which can be downloaded, or purchase the paperback copy. The prices are very reasonable. A medium Cubloc setup will run about $100.00 They have starter kits with everything necessary to set up a working Modbus system with Potentiometers, pushbuttons, LED's, Serial ports for programming and communication.

The other Modbus system I have used is the Arduino single board computer. If you have not looked at, or used the Arduino it is a complete system of boards using a version of "C", to do amazing stuff with your computer. It is known worldwide, and has a huge customer base. The array of boards is quite large, and many different companies make them under license. The original Arduino ran at 8MHz, but the more common ones run at 16MHz. The latest versions are using an advanced chip that runs at 85Mhz. The board runs on 5v. The Arduino forum is an excellent source of engineering/electronic advice by knowledgable experts. The basic Arduino board can communicate with Mach3 through the USB port using a version of Modbus available on this forum. The basic boards cost from $35.00 US to 65.00. The Arduino Mega 2560 has over 50 I/O ports, including 15 analog/serial, and PWM conversion. The Arduino Modbus setup is probably the lowest cost way to use Modbus with Mach3, and maybe the easiest. Some versions of Windows do not run the Arduino IDE properly. The XP works well though. Many of the newest versions of Windows seem to have strange problems though. 

Whatever Modbus you use, the interface to Mach3 will need to use "Brains" to drive the appropriate OEM code.

As with all things in electronics and interfacing devices, there is a learning curve.

John