We have a USB-6218 DAQ and are using the digital output channels to control other devices. When our PC restarts, the digital output lines do not appear to be connected to DGND. A particular device being controlled has an onboard 20K ohm pull up resistor to 5V. I note that the 6218 is specified to have an internal 47 kΩ ±1% pull-down resistor though for some reason when I test it with an ohm meter I see roughly 9.7kΩ. This makes the digital output signal go into a TTL intermediate or high state while the computer is in idle states (e.g. restarting or sleeping).
I've attached a drawing of the electrical setup. And attached a screenshot of what happens to a digital output line during a computer restart (note this is actually with a 22 k ohm pull-up resistor in my test setup).
Questions:
1. Why when I test the resistance on a 6218 between DGND and a Digital Output pin, do I get roughly 9.7kΩ instead of 47 kΩ ±1%?
2. Can someone confirm what I am saying about the digital output lines not being connected to ground when the computer restarts or goes into sleep?
3. How can I wire this system to keep the signal in a Low state and conform to the specifications of the 6218 and the load?
