Epson TM-U590 Technical Reference Manual page 32

Y connection
This printer is connected to the host computer via the serial port. When a customer display
(DM-D) is to be connected, connect it to the printer via the modular cable.
A mount type customer display can be directly installed on the printer.
Connecting the serial interface (RS-232C) cable
Be sure to turn off the power supply for both the printer and host computer before
connecting the cables.
WARNING
1
Insert the interface cable connector firmly into the interface connector
on the connector panel.
2
When using connectors equipped with screws, tighten them to secure
the connectors firmly.
3
When using interface cables equipped with a grounding line, attach the
ground line to the screw hole marked "FG" on the printer.
4
Connect the other end of the interface cable to the host computer.
32
DM-D (Mount type)
Serial cable
TM-U590
DM-D (Stand type)
Modular cable
Modular cable
Cash drawer