In some cases, depending on your operating system requirements and/or your device requirements, it may be necessary for the Data Carrier Detect (DCD) signal to be active on a port before it will function.
There are two ways to fulfill this requirement.
One way to fulfill the DCD requirement is to create a cable and have your device force the signal high. See the Digi One RealPort and PortServer Cable Guide.
Another way to fulfill the DCD requirement is to enable the forcedcd ditty-rp option. See Setting TTY Options.