Apple PC Compatibility Card - Manual (Page 187)

Configuring the PC serial ports
Your PC Compatibility Card supports two serial ports, COM1 and COM2.
You can assign these ports to Macintosh serial ports (such as the printer or
modem port) or to a text file for later processing. Or you can leave the
ports unassigned.
Note: If you are using the optional PC Serial and Parallel Card to connect a
printer, modem, or other device to the PC environment, you do not need to
configure the Macintosh serial ports. See the manual that came with the PC
Serial and Parallel Port card for additional information.
187 Setting Up the PC Environment
Unassigned Macintosh serial port
Macintosh modem port assigned
to COM1 in the PC environment