nect a 5V power supply to DGND and intermittantly touch the currnt supply to DIO1 no change occurs, yet if I leave a variable power supply connected to it and change the Dc voltage from 0 to 5 the digital state changes when I cross the 1.5+ Volt threshold?The digital lines of the 6023E are TTL logic lines meant to handle voltages. You can consider a digital input to be high impedance, basically accepting little or no current. This would explain why your current supply doesn't cause a change in the digital state. The signal must reach TTL logic levels in order to trigger a change in the digital state.
TTL logic specifies the low voltage range (0) to be between 0V - 0.8V, and the high voltage range (1) to be between 2V -5V. Anything not in these ranges, for instance 1.5V, will give you an unpredictable result.
