Lexmark 2390 003 - B/W Dot-matrix Printer Service Manual page 23

Switch 9 - Protocol:
Selects the type of protocol. Differs depending on which serial
interface unit is installed.
Snap-On and Gray Units
Switch 9
Off
On
Black Units
Switch 4
Off
Off
On
Off
Note: DTR protocol is for RS-232C only.
Switch 10 - Print Test (All Units):
Selects the print test for the serial interface adapter. Refer to "Serial
Interface Adapter Print Test" on page 3-6.
Switch 10
Off
On
Snap-On
XON/XOFF
DTR pacing (RS232 only)
Switch 9
On
Off
Off
On
Print Test
Normal mode
Test mode
Protocol
Gray
DTR Pacing (RS232 only)
XON/XOFF
Protocol
XON/XOFF
DTR pacing (RS232 only)
DTR + XON/XOFF
Robust XON/XOFF
General Information 1-11