Yaskawa incremental encoder and Mesa 7i48

I am in a process of retrofitting Biesse Rover cnc machine to LinuxCNC and now Iam up to getting encoder signals read directly by LinuxCNC via 7i48 board (so far I was using the original drives that output the encoder signal to cnc controls).I started with Y axis motor - Yaskawa USAGED-13A22 motor with UTOPH-81AWF encoder (it has 8192 CPR).
What I did was ordering a matching plug from ebay and soldered 8-leadwire to it while other end of the wire was connected to plug on 7i48 so the original wiring of encoder is intact and I can always plug it back in original drive.I am not totally sure that the wiring on 7i48 is 100% correct because the original documentation of the machine does not show meaning of pins: 


So I did some guestimate there according to servodrive manual that mentions channel A, channel B and channel C. 


Channels A and B seem to work exactly as expected - I get approximately 32K rawcounts per revolution (I did not measure very precisely start and end position) but supposed index channel is living its own life. I did some video:

I thought that my adapter wiring is wrong. Checked with multimeter butthere are no shorts between any 2 wires. Plugged back in original drive - everything works and I get nice index pulse once per turn so it seems that this is the way it is supposed to work.I also found this thread mentioning that Yaskawa 5V encoder has to be decoded.  www.forum.linuxcnc.org/27-driver-boards/...coders-plug-and-play
I have yet to understand what is there to decode for incremental encoder (that is supposed to be incremental because of digit "2" right after letter "A" in the name of motor) if both phases have quadrature signal but that is rethorical question.

It seems strange that servodrive manual would name the third channel as "channel Z" for absolute encoder and "channel C" for incremental encoder given that standard designation for index pulse is letter Z. 


What are my options at this point? All I need is an index pulse for BLDC module to home the rotor and get the phase alignment right. I do not even need the index for homing joints, that is optional.

It seems mis-wired to me.

You might verify that you get a sensible voltage
(say about +4V or -4V) in both polarities  when
measured across the pairs (A to /A and B to /B and C to /C),
For all positions (and never a voltage close to 0)

A voltage across a pair close to 0 means a mis-wiring
 

Actually I had checked with multimeter - ALL pairs had 3,3V on one and 0,5V on the other wire. and vice versa when HalShow reported that the pin value has changed.
I googled for rs 422 voltage levels and this picture came up:
advcloudfiles.advantech.com/cms/2fde048f...ge-1540322331041.jpg

According to last line everything is correct at the moment, so I do not even understand where to start to look for miswire - all the pairs behave the same.
Am I missing something and is that picture wrong?

You really need to measure _across_ the pairs
to validate the wiring

A long time ago I tinkered with some Yaskawa drives and motor/encoders. What I THINK they do is change the phase between the A-B and C channels to indicate what quadrant the motor is in, and that allows them to detect the proper commutation to use to move from that position. So, the A and B are perfectly standard quadrature, but the C channel has transitions at the same rate as the A or B channel, but the phase gives additional information.
Jon

I vaguely remember seeing that one
The documentation I looked at had C=index
(and S = serial absolute position)
but that must be a different model

If that's the case, you will likely need
to use plain q mode (magnetic alignment)
rather than QI mode