The problem is the person who designed the hardware some years back and fortunately left only three pins free out of them two were hardware interrupts Pin 12 & 13:-),
and now I am suppose to interface the encoder with this limitation only as the circuit has to be a field replacement.

Only relif I have is, I dont have to count in both directions. This is a liquid flow measuring device so only outword flow is to counted as they have taken care mechanically that the liquid will never flow in reverse direction.?!


So I think I have only option of a=clk and b=input.

Any more ideas;-(

Thanks,
Sachin