Spin motor in both directions..n...Verilog code

HI i need help writing a verilog code for a motor that will spin in both direction ( forward and backward), I have already generated a PWM signal to spin and control the speed of the motor using 8 switches but i cant figure out how to control the direction of the motor. i m using a basys 2 fpga board for this project. I will appreciate all the help i can get. thank you