Lexmark Optra E 4026-0 Series Reference Handbook page 169

Optional I/O Device Interface
Pin Signal
1 /TX
2 GND
3 /RX
4 /TERMINATE
5 +24V
6 /CLOCK
7 GND
8 GND
9 GND (KEY)
10 +24V
11 GND
12 /STROBE
13 PWRON
14 GND
15 +24V
6-42
Laser Printer Reference Handbook
Signal Name
Send Data Line
Receive Data Line
Communication Ready Signal
Synchronized Clock Signal
Mis-insertion prevention
Strobe Signal
Power On Signal