Two wire stepper motor Control with PIC MCU (16F877A)

Only two wires are needed to control a stepper motor by a PIC .It is very much useful when number of available I/O pins are limited .The conventional stepper motor control needs four wires.Only the thing I have done is design a simple 2 to 4 decoder and use it in between the PIC and stepper driver(ULN2003A).

So the logic expressions are as follows.
   P=B'
   Q=A xor B
   R=B
   S= A xnor B = (A xor B)'

So implemented codes and diagrams can be downloaded from here. MikroC was used for programming and for simulations Proteus was used , the implemented circuit works nicely.

Please comment your ideas.