Metasys Passthrough Mode - Interim Solution

The S4 Group has a fully integrated replacement for Metasys Passthrough Mode support under development for our S4 Open Management Console that will support both the S4 Open: BACnet-N2 Router and the S4 Open: OPC-N2 Router. There is so much demand for this capability that we decided to investigate if there was an interim solution available until our development work is complete. There is. Even though the user experience is not nearly as good as our final product will be, this approach still gets the job done.

This approach leverages the capabilities of the S4 Open Appliance Upstream Interface, which provides a virtualization of all the devices on the N2 bus. The S4 Open Appliance ensures the integrity of transactions originating both from the BACnet or OPC interfaces and the Upstream N2 interface.

We ended used products from B&B Electronics but feel free to choose your favorite technology and test carefully before deploying in a production environmnet.


Step 1: Install a B&B 485USBTB-2W USB to RS-485 adapter in the PC that will be used as the Engineering Workstation. It needs to be set up as either COM1 or COM2.

Step 2: Set up one B&B VESP 211 serial server “EngrWorkstation” as the client side of a paired connection. Connect it to the serial port of the 485USBTB-2W. The serial port needs to be set up for RS-485 2-wire operation.

Note: The first two steps are a work-around. I would have preferred to use a virtual COM port instead. However, after testing multiple products from various manufacturers, a combination of issues with assigning COM1 or COM2 or compatibility of HVAC Pro with the virtual COM port technology led us to this approach.

Step 3: Set up one B&B VESP 211 serial server “N2NetworkXX” as the server side of a paired connection. Connect it to the Upstream N2 interface of each N2 Router. The serial port needs to be set up for RS-485 2-wire operation.

Step 4: Load the M-Tools package on the Engineering Workstation PC. M-Tools can be purchased through JCI authorized ABCS distributors.


Run the Vlinx Serial Server Manager and perform a Server Search to find all Serial Servers on the network.

Open the EngrWorkstation serial Server and enter the IP address of the N2Network serial server that you want to pair it with.

Save the configuration and allow the serial server to restart.

Now use HVAC Pro or GX9100 as you normally would selecting the COM port (COM1 or COM2) that you configured for the 485USBTB-2W adapter.

Note 1: The only limitation that we have found is that you have to disable the BACnet traffic in the S4 Open: BACnet-N2 Router if you are performing Upload or Download operations to a N2 device. Any other operation works fine without taking this step. After your Upload or Download is completed don't forget to re-enable BACnet communications. In our implementation of Passthrough under development this process will be automated. 

Note 2: This approach has worked on both a Windows XP machine and a Windows 7 machine as long as it is 32-bit. One of our integration partners who reviewed our work volunteered that HVAC Pro will also work on a 64-bit WIndows 7 machine utilizing XP Mode.