Epson PLQ-20 Reference Manual page 82

* When the printer turns on in Auto I/F mode and PR2 mode, this mode is set
to Serial.
** When the printer turns on in the PR2 mode, Packet mode is set Off.
Software
This setting allows you to select the software format. When you
select ESC/P2, the printer operates in the EPSON ESC/P mode.
When you select PR2 or IBM PPDS, the printer emulates an Olivetti
or IBM printer.
High speed draft
In PR2 mode, this option is available in any pitch.
In other modes, this option is available when the pitch is 10 or 12
cpi (characters per inch). When you choose On, the printer prints
up to 480 cps (characters per second) at 10 cpi. When you choose
Off, the printer prints up to 360 cps at 10 cpi.
I/F mode
The printer provides built-in slots for three kinds of interfaces;
Parallel, Serial, and USB. You can choose Auto (automatic),
Parallel, Serial, or USB, for the interface mode. When you select
Auto, the printer automatically selects the interface that is
receiving data, and uses that interface until the end of the print
job. The Auto setting allows you to share the printer among
multiple computers without changing the interface mode. When
the printer turns on in Auto I/F mode and PR2 mode, this mode
is set to Serial.
If only one computer is connected to the printer, you can select
Parallel, Serial, or USB depending on which interface your
computer uses.
Chapter 5 Control Panel 82