Digital I/O
Problem with TriState on DI pin
Hi all!
I 'm having a problem using my DAQ device, probably just due to my lack of knowledge, but hopefully by the help of this great forum I'll have it solved;
My DUT have a bi-directional pin which is used during startup (by the DUT) to decide what operational mode to run in. I have connected this pin to a AI chan. just to monitor what's happening during startup, this works great. I'm sampling the AI chan and triggering off the DUT supply voltage. I also want to hook up a DI chan to this pin because in some cases I want to trigger the sampling off of this pin (when it goes high).
Heres where my problem arises: I've connected PFI1/P1.1 to the bi-directional pin of my DUT. I've also used the "DAQmxTristateOutputTerm()" to make certain the DI chan is configured with high impedance. The problem is that this causes my DUT to power up in the wrong mode.
I've observed the following (lets say I have operational mode 1 & 2):
- DUT not connected to PFI1 -> operational mode 1 (as expected)
- DUT connected to PFI1 and PFI1 set high -> operational mode 1 (as expected)
- DUT connected to PFI1 and PFI1 set low -> operational mode 2 (as expected)
- DUT connected to PFI1 and PFI1 set to tristate -> operational mode 2 (not expected)
As I have understood this, using tristate should cause the DUT to "see the pin as not connected" (i.e. high impedance) thus starting up in mode 1 as it does when PFI1 is not connected. But this is obviously not the case.
Can anyone explain this behavior to me?
Theres definitively something I've misunderstood here
Using:
NI USB-6251
LabWindows/CVI 8.5
I 'm having a problem using my DAQ device, probably just due to my lack of knowledge, but hopefully by the help of this great forum I'll have it solved;
My DUT have a bi-directional pin which is used during startup (by the DUT) to decide what operational mode to run in. I have connected this pin to a AI chan. just to monitor what's happening during startup, this works great. I'm sampling the AI chan and triggering off the DUT supply voltage. I also want to hook up a DI chan to this pin because in some cases I want to trigger the sampling off of this pin (when it goes high).
Heres where my problem arises: I've connected PFI1/P1.1 to the bi-directional pin of my DUT. I've also used the "DAQmxTristateOutputTerm()" to make certain the DI chan is configured with high impedance. The problem is that this causes my DUT to power up in the wrong mode.
I've observed the following (lets say I have operational mode 1 & 2):
- DUT not connected to PFI1 -> operational mode 1 (as expected)
- DUT connected to PFI1 and PFI1 set high -> operational mode 1 (as expected)
- DUT connected to PFI1 and PFI1 set low -> operational mode 2 (as expected)
- DUT connected to PFI1 and PFI1 set to tristate -> operational mode 2 (not expected)
As I have understood this, using tristate should cause the DUT to "see the pin as not connected" (i.e. high impedance) thus starting up in mode 1 as it does when PFI1 is not connected. But this is obviously not the case.
Can anyone explain this behavior to me?
Theres definitively something I've misunderstood here
Using:
NI USB-6251
LabWindows/CVI 8.5
