For automatic tests I am using a NI USB-6211 device for generating e measuring analog and digital signal. I noticed a behaviour that I want to understand.
The device is connected to a circuit which work as an interface for linking to the system to test.
When I connect the serial port of the USB-6211 to my PC all the digital ports start to generate at +5V (I have controlled with an oscilloscope). I have also checked from the device Test Panel and it shows that all the output ports are off (so they have to be at 0V). The annoying thing is that each time, before starting the tests I have to turn off all the ports and then start testing. It is problem for me also because this test bench is not used only by me.
I don’t know if this is a normal behaviour of the device or if there is something that I don’ know, so every kind of help is really appreciated.
Thank you for your advices and helps!
You mentioned Serial port, but I will assume it as a typo and consider as USB.
As per the user manual of USB-6211, on power-up, all the ports are high-impedance with a weak pulldown (47k). This means, if your other side of the connections has a pull-up stronger than 47k to 5V, it will appear as 5V.
Does this happen even when the 6211 is disconnected from the external circuit?
Thank you very much santo_13 for your precise answer!
The device takes its power supply from my PC with a USB A/B 2.0 cable, the external circuit is only for the connection to the electronics parts under test and it is powered by a 24V from an external source. It’s the connection to my PC that cause the generation of the 5V even if the ports are all disabled on the USB-6211.
If my information is incomplete or not precise, I ask you to be patient because I’m pretty new in this world.
However, for the moment I create a small VI for setting all the outputs ports to 0. It’ only a work around till I understand the things better.
Let me ask one last thing that I didn’t read in the manual, the digital output of the USB-6211 as default are configurated as an open-collector/open-drain or as push-pull?