Two channel Quadrature encoder on parallel port

Apologies if something wrong this is my first topic.
Can someone please help newbie, and explain if (how) possible to use only TWO ( A and B NO Z index) channel quadrature encoder on parallel port .
Encoder fitted to brushed DC Motor, with PWM + Direction drive also on parallel port.
This is test setup and don't need super performance.
Just stumble into luck of Z output from encoder and seems to me Linuxcnc can't close servo loop without?
Many thanks in advance

Sure, just need 4 free input pins on a parallel port or other input device
(you can have up to 8 software encoders)

man encoder

In a terminal window will display the encoder manual page

Thanks Guys for input
I kinda feel LinuxCNC need this I with is Index signal from encoder? My question is can LinuxCNC PID loop tune with out this Index I output from encoder ( my particular encoder does not have I only A and B outputs)
Many thanks
Ilia

Index is not needed for tuning

encoder index signals are used for two things in linuxcnc:

1. More precise homing of axis
2 Spindle synchronized motion like threading or rigid tapping (spindle encoder)