SSI encoder

hi all,I have an ABS encoder, CAX60.My config in linuxcnc

loadrt hm2_eth board_ip="10.10.10.10" config=" num_encoders=0  num_stepgens=6  ssi_chan_0=ENC_ZH%24eENC_SIGN_Z%1b 

# set speed
setp hm2_7i80.0.dpll.02.timer-us -300

setp hm2_7i80.0.ssi.00.frequency-khz 125  
setp hm2_7i80.0.ssi.00.timer-number 2
setp hm2_7i80.0.ssi.00.ENC_ZH.counts-per-rev 4096
setp hm2_7i80.0.ssi.00.ENC_ZH.scale -32.25

However, I received a random encode value. 
At home position:
When I open the linuxcnc and turn on power, I get the 0 value of encoder. 
But sometimes i turn on linuxcn at this position and i get 250 value of encoder.

can you hel me check my config is correctly?

thank you so much

Is the problem just the startup value, or does it not give useful output either?
ie, is it _always_ random, or just at startup?

It is simply random when starting up. 
thank you so much

I would first try all 4 combinations of polarity

(all 4 combinations of swapped CLK+ and CLK- and swapped DATA+and DATA-)

Also its hard to tell from the awful data sheet, but it seems to be a Gray
coded encoder so your format string may not be correct.

Could you possibly give me a format for this encoder? i will test it tomorrow.

Thank you for your help.

Apart from the startup value, does the position otherwise work, ie increases smoothly without jumps as it is turned?