XC-23 minimum input voltage

Hello,

I have an H-Bridge that drives a DC brushed motor on 12V. I need to determine the PWM ratio being supplied to this motor by the H-Bridge. There is no other signal that could get me this information so I am contemplating hooking both sides of this motor to PWM inputs on the XC-23. Before doing such a thing, I looked at the signal using an oscilloscope. Basically, the signal is 0-12V most of the time but dips below 0V when the ON time finishes. The lowest voltage read with the scope is -11V for a short period of time.

There are no Absolute Requirements for negative voltages on inputs in the datasheet of the XC-23. What is the absolute minimum voltage that can be applied to a PWM input of the XC-23 without damaging it ?

Guillaume