Encoder Wiring question Is GND Needed

I'm having trouble getting linuxcnc to read me servo driver simulated encoder output.
I have wired A /A B /B Z /Z to the 7i77 encoder terminals, but not getting any counts.
+5 and GND are disconnected.

Does encoder GND need to be connected to the drive at all?
I thought being differential outputs, the A /A are referenced to each other?

I have tried checking with a voltmeter between the A /A pins on the drive, while spinning the motor (slowly), but getting nothing.
I have an oscilloscope I will try to get hooked up this weeked to check for sure.

My feeling is I have a problem in the driver settings or the driver itself, just wondering if someone says Yes, the GND must be connected somewhere.

thanks.

I hope I read you correctly, if so then the +5v supply and ground must be connected from the encoder to the 7i77 or your encoder is not getting any power as a result. The drive should be inconsequential in this matter.

1 QA0 TO 7I77
2 /QA0 TO 7I77
3 GND FROM 7I77 <---GROUND
4 QB0 TO 7I77
5 /QB0 TO 7I77
6 +5V FROM 7I77 <--- +5
7 IDX0 TO 7I77
8 /IDX0 TO 7I77

Thanks.. I guess I should have given more info.
The encoder is powered by the servo drive and uses serial communication.
The drive then has a "simulated" quadrature encoder output.
It has the usual A /A B /B Z /Z and an extra OCZ (open collector output)
I think I know the answer, that is my drive is messed up, or I am overlooking some setting.

I'll keep messing with it and hopefully it will work, otherwise I'll have to sell this 7i77 and get a 7i76
Oh well..

Ugh... many hours wasted because of a bad cable, I wired up another one and I am getting results now..

Thanks for the help