Epson 500 Series - Manual (Page 51)

5. Connect the other end of the cable to the printer. If the printer
interface has retaining clips, squeeze them gently until they
snap into place.
6. Connect the printer's power cable to a grounded electrical
socket.
Connecting a Serial Device
You can use the COM1 port to connect a serial device. such as a
serial printer or plotter. You could also connect a modem or
pointing device, such as a trackball or mouse.
Follow these steps to connect a serial device:
1. Make sure both the computer and the serial device are off.
2. Connect the serial cable to the COM1 port.
3. If the connector has retaining screws, tighten them by hand
or with a screwdriver.
4-6 Connecting Optional Devices