Apple LaserWriter 12/640 PS - Manual (Page 267)

You make changes to the communication settings with the printer’s
communication switch set in the Normal (in) position. This makes all
communication settings available for changes.
For more information about connecting the printer to LocalTalk, Ethernet,
and parallel ports, see “Connecting the Printer” in Chapter 1. For more
information about setting the communication switch on the printer, see
“Adjusting Communication Settings” in Chapter 1.
1 Set the communication switch on the printer to the Normal (in) position.
2 Open the Communication Configuration category.
You see a list of communication settings options.
3 Open the Port Configuration category.
A list of port connections and protocol choices appears.
267 Setting the Printer Default Settings