Stepper motors don't use PWM. Did you mean DC motors here?
Either I didn't understand fundamental things or I was not precise enough:
I meant that the BigEasy-Drivers need PWM as input if stepper-motors are to be steered.I found an example http://bildr.org/2012/11/big-easy-driver-arduino/
where one PWM-Pin is connected to the BigEasyDriver inputs while the other input Pin is connected to a normal digital output (direction).
But if a steppermotor only needs two digital inputs, everything would be more easy because the Mega2560 has much simple digital pins.
Do BigEasyDriver need PWM-Outputs for steering stepper-Motors?