WT901B | manual v0707 | http://wiki.wit-motion.com/english
For digital input mode, if the voltage is high, DxStatus=1, else, DxStatus=0.
For digital output mode:
Voltage is high, DxStatus=1.
Voltage is low, DxStatus=0.
PWM output mode is used for the output of the PWM wave, the cycle and the
high level width can be adjusted, the unit is us. In the PWM output mode, the
port state data is used to indicate the high level of the PWM, the unit us.