rotary encoder with arduino and matlab

hi

I am using a Rotar Encoder when I want to read the count of the encoder pulses in one direction it works good but when I turn the encoder shaft to the other direction the counting won't be decreasing and it would be increasing!!!!

this is the code that I write:

a=arduino('com9','uno','Libraries','RotaryEncoder');
encoder=rotaryEncoder(a,'D2','D3');
for i=1:1000
    count=readCount(encoder);
    fprintf('count: %d\n',count);
    pause(1)
end

and this is the data sheet of the encoder:

encoder