Epson 386/25 - Manual (Page 31)

Using the Serial Interface
If you have a printer, a modem, or other peripheral with a serial
interface, you can connect it to the serial (RS-232C) port on
the back of the computer.
The serial port uses a DB-9P connector, so be sure you have a
compatible cable. To connect a serial device, follow the same
steps as above for connecting a parallel device but insert the
connector into the serial port, marked with a special icon, as
shown below.
Setting Up Your System 1-11