Apple LaserWriter 12/640 PS - Manual (Page 277)

m You can set the TCP/IP interface to PostScript mode, PCL5 mode,
AutoSelect mode (which automatically senses whether PostScript or PCL5
mode should be selected), or turn it off.
IMPORTANT If you select the On mode setting to turn on the EtherTalk,
NetWare, or TCP/IP interface, the change does not take effect until the printer
is turned off and back on again.
3 Click Set Port.
Resetting communication settings
To restore the communication settings to the factory defaults:
1 Set the communication switch on the printer to the Reset (out) position.
2 Turn the printer off and back on again.
3 Set the communication switch on the printer to the Normal (in) position.
Communication
switch
277 Setting the Printer Default Settings