Epson 7500 - Manual (Page 20)

Using the Serial Ports
If you have a printer, a modem, or other peripheral device with
a serial interface, you can connect it to one of the serial
(RS-232C) ports on the back of the computer. These ports use a
DB-9P connector, so be sure you have a compatible cable.
To connect a serial device, insert the connector into one of the
ports, marked SERIAL 1 and SERIAL 2. If you are connecting only
one serial device, use the SERIAL 1 port, as shown below.
SERIAL 1
Setting Up Your System 1-9