I need to fulfill the requirements of using P16F877, LM18298 h-bridge and PWM to make 2 DC motor go forward, backward and reverse. But i got minimum knowledge on this so need some help....
You can role down this datasheet, and see the application information. You can make the circuit.
To turn the motor, you make pin3 and pin4 High/Low or Low/High.
But if you do so, you cannot control the velocity of the motor.
PWM help you this.
As you intend to make pin3 HIGH, and pin4 LOW, you give a pulse to pin3 with period upto 5KHz and the duty cycle can be open from 0 to 100% on pin3. This make your motor turn as pin3 HIGH, pin4LOW, but at lower speed. However, as you open duty cycle from 0% to 100%, you can control the velocity of the motor from stop to run at max speed.