Today is...
Thursday, May 23, 2019
Welcome to the Modbus Community, about
the world's leading automation protocol.
PACTWare communication with a Remote RS232
Communication with a remote MODBUS device over TCP/IP

Hey community,

I have the following equipment:

- Measurement Instrument VEGAPULS 61 with usb modbus RTU
- Router with RS232 DB9. Router is MODBUS capable and can be master or slave.
- PC with PACTWare + a Utility for creating Virtual Serial Ports.

I have connected my VEGAPULS 61 to the routers RS232 port with a USB to RS232 adapter. I have configured MODBUS on the router to user serial port COM0. I have configured a virtual COM port on my device, COM4.

Started PACTware and started a RS232 scan. It connects to COM4 and sends data and receives data. All I got that the device is not supported.

Has anybody tried to access a MODBUS RTU remotely from a Virtual serial port that points to an IP:PORT, please?


I'm not sure what a 'router' with a Modbus master is. What would a Modbus master router do with the data received from a slave? Route it to another slave?

And if Pactware connected through COM4 (232), how did it send and receive data, yet 'the device is not supported'? The two statements contradict one another.

I read through the Vegapuls 61 manual and its Modbus RTU over RS-485 appears conventional.

As far as I can tell, the radar's USB port is not affiliated with Modbus, except for configuration of RS-485 serial port.

To my knowledge, Pactware is configuration and troubleshooting software (on the dozens of instruments I've used it with). I do not believe that Vega's DTM for Pactware includes Modbus master functionality for purposes of data exchange, although anything's possible.

The Vegapuls manual section 7.3 provides 3 different techniques for changing the Modbus slave node address for the radar unit, because the integral push-buttons/display, which otherwise do set-up operations, do not have the ability to change the Modbus slave node address.

One of the methods of changing the Modbus slave node address is using Pactware. I did not read the manual completely so I'm not sure what Vega's method is for communication with Pactware with this unit. It might be HART (but HART needs a 4-20mA signal to ride on) or maybe that is what the radar unit's USB port is - a means of connecting the radar unit to Pactware.

A generic Windows Modbus master program (like Modscan or Modpoll or any of the others) with a USB/RS-485 modem can also be used, by writing a value to Modbus register 200. That same Master/modem could be used to read the level process variable.

If you're expecting Pactware act as a Modbus master and to poll the radar and do something with the data, I'm doubtful that Pactware's DTM file is that powerful.

Thank you for your answer.

The router software supports legacy protocols such as MODBUS. The router can be configured to be a MODBUS master or a MODBUS slave. I connected the VEGAPULS 61 via USB to the router. It recognized it, but did not create an ASY device for communication, because it does not know how to talk to a HART modem. The other alternative I had was to convert USB to RS232/RS485 and connect it to the serial port of the router. In PACTWare I have the options to scan for devices connected to:

- RS232. Since the VEGAPULS is remote, I need to create a local virtual port on the PC, so PACTWARE think that the VEGAPULS is locally connected. The Virtual Serial port software sends the serial communication over the internet to the router and router decapsulate it and send it the RS485 port.

- USB. Not a good option for my scenario. My router does not understand HART.

- TCP/IP (LAN). It does not allow one to scan for a specific IP and port.

- Bluetooth. Not an option. VEGAPULS in fields are hundreds of kilometers away.

So again how can I make pactware to talk a VEGAPULS connected to a remote serial port over TCP/IP. Thanks.

Kind regards,