Correct way to drive the L6203 Full Bridge driver
You need to put a PWM signal on IN1 and gnd IN2, to have to motor run to the right side for example. (This ensures that the left upper MOSFET is in conduction with the PWM and the right bottom MOSFET keeps conducting because of the inversed AND input from IN2)

If you want the motor the other way, then put a PWM signal on IN2 and gnd IN1. The the right upper MOSFET wil conduct according to the PWM and the left bottom MOSFET keeps conducting because of the inversed AND input from IN1.

Note, if you want to enable the driver the enable pin must set high. If you want to disable it then put it to GND.

PS: If you don't want to mess up your µC then use some buffers (schmitt-triggers) to protect your µC.

Goodluck.