The G540 has opto isolators whose LED inputs have internal pull-ups to +12 volts.

Your sensor boards and the A180 device on them are strictly 5 volt devices. When
you tie their outputs to the G540 there is leakage current from the G540 even when
the hall sensor is in the off state because the sensor output will not pull up much
above 5 volts. You will need to buffer them or choose a different sensor.

Steve Stallings
PMDX.COM - Products for CNC and motion control applications