The engine works but only in one direction

[Marfon]

Hi everyone,
it's m.y first time writing in this forum.
My name's Luca, i'm 30 and i'm italian. I've finally done my first test with my Pluto-p, in configuration lathe-pluto, at the moment with just one engine.
As a h-bridge i've used the 298 one . I've linked the pluto pin 28 and 29 to the encoder, the pin 20 to input 1 and 21 to h-bridge enable.
I send to input 2 the opposite signal of input 1 with a not.
Everything seems to work! The pid works only if i rotate the engine in one sense. Measuring the voltage with the tester on the pwm pin, it varies from 0to 3,3 v, and it doesn't happen if i rotate the engine in the opposite sense: on the pwm pin i have 0 v.and the pid doesn't work.
Can you help me suggesting some solution?
Thank you
Luca