The optical encoder has two channels (A & B channel). The encoder send pulses as the encoder shaft turn clockwise and anti-clockwise. When the encoder turn clockwise, A lead B. When I turn anti-clockwise B when lead A.

A lead B by electrically 90 degree.
B lead A by electrically 90 degree.

I am doing a interfacing the encoder with a expanded mode 8051 controller card and display on seven segment LCDs. How can I make the clockwise direction to INCREMENT and anti-clockwise to DECREMENT.

Can someone give me some idea how to do it. Thanks......