Hello,
I am having trouble working with this circuit (see the picture). It is supposed to be a DCC train decoder. I am decoding a signal from the power line and then using the attiny to control a motor with a DRV8251 motor driver. Everything is working absolutely fine, except that the motor runs much slower in one direction than the other. After some measurements, the h-bridge outputs a much lower voltage in one direction. I have tried replacing the H-bridge and even all the components. Tried measuring the voltage on IN1 and IN2 of the H-bridge, the voltage is the same in both directions. Could someone give me advice? This starts to drive me mad. Even with an oscilloscope, I can't find the problem

 

Struggling to follow the control signal and control scheme thru the collection of snippets.
If, as stated, the "H" bridge outputs a lower voltage in one direction than the other, the obvious question is about the two inputs that control the "H" bridge.
ALSO, a question: are the input signals analog DC, or are they PWM signals?? IF they are PWM signals the an analog meter will show the same value while the duty cycle will be much different.

 

Sounds to me the motor is drawing much more current in one direction than the other. Measure the DC current into the motor in both directions when just powered by the supply, no H-bridge.

 

It is entirely likely that Irving has the correct answer in post #2
My suggestion now is to first, measure the supply voltage to the H bridge as the motor is driven in both directions. If the voltage drops more in one direction, then the problem is in the supply. If the voltage does stays the same driving in both directions, then the problem is probably in the PWM control signal.
For many motor applications the load is quite different in opposite directions.