The Metasys N2 bus follows the RS-485 standard for its physical and electrical characteristics. It runs at 9600 BD, half duplex using N2+, N2-, and Ref wires. Our S4 Open appliances are pre-configured to have all Com ports operate in RS-485 mode.
If you run any of the JCI Metasys configuration or commissioning tools HVAC Pro, GX-9100, etc. from your labtop or another Windows PC and want them to communicate the the N2 bus via their COM port you'll have to utilize either a USB to RS-485 or a RS-232 to RS-485 converter.
We have been using RS-485 converters from B&B Electronics www.bb-elec.com to connect our PCs to the N2 bus.
For RS-232 to RS-485 we use their model 485SD9TB
For USB to RS-485 (N2 bus) we use their model number 485USBTB-2W
The USB Serial Port technology has become so standardized that most manufacturers' products should work fine although the B&B products are the only ones we have tested. Note that you may have to adjust the COM port assignments for some versions of HVAC Pro because it only allows you to configure to COM1 or COM2.