have set it to 0 but i could not see any changes in RM value it shows same.

in general configation i saw there 8 bit one stop for serial output.

i dont know exact where i can find a bit about index pulse?

can u please guide me?

I am asking what hardware you are using for the index pulse, ie is it a slotted disc with an optical sensor?
Hood

i m using proximetry sensor

Does the spindle speed show correctly in Mach when you have it running?

Ok another question, in your PM you said you want to thread 500m but I am not sure what you mean, are you meaning a length of 500mm or?
Hood

when i use parrallel port that time spindle RPM shows correctly i told you i can thread 150 mm long length for longitudnal 6 mm pitch.

on parrallel port i cant do thread up to 500mm length and 5mm pitch. because after 150 mm length thread pitch shift. so i prefered to use SS.

Does the RPM show correctly with the SS?
Hood

yes it shows correct RPM

Ok I am needing to understand a bit more about what your problem actually is. I realise English is not your native language so it is not so easy for you but likewise it is not so easy for me to understand what is actually happening.
You say
"my threading stop while running for 1 or 2 second therefore threading pitch shift." Do you mean the SmoothStepper faults or does the threading just stop and stand still?
Are there any error messages?
Does the SS lock up?
Hood

no there is no any fault in smooth stepper.threading stop for one second in first depth of cut and continue withine second same cycle because of that our threading pitch shift in second depth of cut of cycle. this kind of thing happen every depth of cut. i changed ss board but same problem also. as well as i replaced ram of pc 1GB to 2Gb

What RPM are you threading at?
Hood