To set the serial port:

Choose Newton Connection > Preferences.

Select the serial port in the pop-up menu.

Close the Preferences window.
To use a serial connection you need a serial cable to connect your Newton device to a serial adapter such as the Keyspan USA-28X, which is in turn connected to a USB port on your computer. Follow the instructions that came with your USB to serial adapter to install any necessary software on your computer.
The first time you use Newton Connection with a serial connection you need to specify how the Newton device is connected to your computer.
Choose Newton Connection > Preferences.
Select the serial port in the pop-up menu.
Close the Preferences window.