Pixracer/pixhawk with XL-5 ESC

Hi everyone,

I’m trying to drive a XL-5 ESC. Now I can make it forward in both mode 1 sport mode and mode 3 training mode. But I never can make it reverse in neither mode 1 nor mode 3. The PWM rate is 50Hz or 100Hz. The pulse width is from 1ms to 2ms.

Any suggestion?

Many thanks!