Rotary encoder with PXI system

Hi,

I'm using PXI-6225 to measure the rotary encoder.

Rotary encoder:

14bits SSI, grey code.

Spec: http://www.roundssencoder.com/news_images/20150729020449903.pdf

Hardware connection:

-Connect the PFI12 (clock source) to PFI0 and PFI8 with 100Khz Actual Frequency

-Connect the P0.0 out to the IC SN75176 pin4(D), the output CLK+ and CLK- to the rotary encoder CLK+/CLK-.

-Connect the rotary connector D+/D- to another IC SN75176 pin6/7(A/B) and D to P0.1.

Software:

As attach.

The system will rotate at 600rpm (10hz), so will continue monitoring every 10ms (100hz).

I able to get back all the correct info from the rotary encoder and display to the oscilloscope (as attach) and at the same time readback from P0.1. 

The problem is I get back all "1" from the reading value.

Can advise for the software what need to modify?

thanks,

Simon