In internal position register mode, the motor will stop
rotating if the signal is active(It can only work when
internal position mode FA-14=3).
In internal position register mode, the signal will be
triggered once the internal position register control
commands(POS0-2) are chosen, and then the motor will
rotate according to the internal position register command.
Only when ZSPD=1(digital output) it would receive a next
internal position command trigger.